I suggest buying used because it opens you up to buying just about anything on the market, well £190 ($300) will quite literally let you buy any universal in existence short maybe the SE535 just because it's so new. £150 ($240) will let you buy a lot though.
The PortaPro is loved for its value and not so terrible sound. The CX-300, well, most people will tell you it sucks...bad. I don't think you'll have a hard time doing better, even for a lot less than £150.
A variety of music typically requires a well balanced or at least not too colored of an earphone. Since you do listen to a bit of synthetic stuff, you may want a product that can do 30Hz or 40Hz tones decently well without needing to add a ton of EQ to get it. For a lot of other stuff, the need to play under 40Hz isn't a big necessity. Vocals don't go that low, nor do most instruments. For techno type music I do tend to prefer very directional sounding earphones. One of my favorites for techno is the Triple.Fi 10. It is colored a bit though, but it is a likable and enjoyable coloration. Most people do find the mids to be a bit recessed though given the earphone is geared with a midbass and treble emphasis. There are more balanced options, but I do bring it up because it's a very fun earphone and especially so with synthetic music.
With drums, you typically look for three things: speed, hit, and body. Basically you don't want the earphone to be sluggish or sloppy. You don't want it to be smoothed over too much. You also want it to be punchy. You want to feel the hit. There should be a sense of power, a whack, that visceral sense of impact. Lastly bass is a low frequency thing and low frequencies are drawn out, hearty, full of presence, weighty. There should be a hearty presence to it, not thin, lean, lifeless. There is always a challenge to get all of this together in the exact way you think of as "ideal." Earphones come in a lot of flavors, and the presentations of any particular sound varies as much as the number of earphones out there. In a basic sense, dynamic earphones typically have a better bass presence than balanced armature earphones, but balanced armature earphones typically are faster. There aren't a lot of options from either camp that do both aspects really well, having excellent presences as well as effortless speed. I will say there are a lot of bassy earphones that I simply have not used. My preferences have been more towards balanced. However, I do see good bass extension and good bass presence as part of balanced. I just want the mids and highs there too and just as well presented. Because of this I have shied away from some of the well known bass earphones due to the fact that they often suffer from poor highs. Some higher end bassy earphones do fair better at covering the spectrum, and I've used a couple of these. The IE8 and UM3X are good examples. Both do bass really well. Both are bass emphasized, but they both do cover the rest of the spectrum well. The end frequency response and presentation may or may not be your ideal, but they do bass well and they aren't hindered much at all through the rest of the spectrum.
For a broad mix earphone, something that has an excellent detail, speed and locational cues that make techno fun, something that is balanced throughout that is capable of playing a broad range of music equally well without need for EQing, and something that has good bass extension, presence, and visceral sense, there just aren't many options out there. One of my favorites and a relatively recent earphone to myself is the Ortofon e-Q7. It is probably one of the best all-around earphones I've used that does a heck of a lot of things well. I can pick out other earphones that excel better at certain things, but as a total package, I see the e-Q7 as the best option out there. New, it's pricey. Used, it's barely within your budget. Their new e-Q5 which uses the same driver is a cheaper version that is near the top end of your budget if you must have new.
Other options I would have you look at would be the Klipsch Custom 3, HifiMan RE252 and RE262, and UE Triple.Fi 10. I'm a big fan of the Custom 3 because Klipsch did really well with the driver choice. The balance and texture is top notch and really does directly compete with top end products at a fraction of the price. They are outstanding earphones that can be had for $100 USD. The cord sucks, but you can later convert them to custom molds and fix that and it'd still be within your budget. The RE252 is very well balanced and has some visceral sense. The RE262 is a better driver, more visceral and clean but more colored and less ideal for a broad spectrum of music. The Triple.Fi 10 is also colored, but in the right ways for techno that does make it very fun. Notes are unusually hearty for a BA setup, and you gain some visceral presence from it. The Triple.Fi 10 is fun and enveloping, colored but also very refined. What about the IE8 and UM3X? Well, I do question how much bass presence you seek. Neither is massively bassy, but they have a more significant focus that sort of makes them always bassy.
A note on the IE8 sound stage comment...
The IE8 has a big sound stage. Big just doesn't make it great. The biggest problem with the way the IE8 presents sound is that it presents ALL sound far away. Near is far. Far is far. This does largely prevent the ability to create layering and separation. Sounds that would normally seem near and far are all over top each other far away. This isn't to say that the IE8 sounds muddled or dirty. No. The sound quality is excellent and clean. It's just that the presentation does have certain limitations. In terms of sound stage, there are significantly better options. The IE8 isn't terrible. It isn't great either. It's just big.
