You should really look at used items from fellow Head-Fiers. Both the SE530 and Triple.Fi 10 can be had more towards the $200-$250 range.
In terms of sound, they are polar opposites. The SE530 is midrange dominant. The Triple.Fi 10 is bass and treble dominant. The SE530 has a very thin note. The Triple.Fi 10 has a very thick note. The SE530 has higher dynamics but less energy. The Triple.Fi 10 is more robust sounding but less dynamic. Both offer a lot of detail. Both have good sound stages although different from each other. Fitment of the SE530 is easy but the cord is rather heavy. The Triple.Fi 10 is harder to fit initially but is more forgetable when wearing. Comply T-500 tips help a lot in getting the Triple.Fi 10 to fit comfortably and seal easily. The other part is just spending time shaping the memory wire right to fit over the ear well and position the earpiece right. With the recessed treble and early bass roll off of the SE530, the SE530 is somewhat limited in what it can do across many genres. The Triple.Fi 10 offers better extension on both the top and bottom of the spectrum. The SE530 is more balanced across the spectrum that it does play and sounds natural and realistic. The Triple.Fi 10 is more V shaped and presents realism in a way I describe as like watching TV. What you hear sounds real, but you know it's an image of that real thing, like watching real people on a TV screen. It's not bad but is less direct. Both are very refined it sound. The SE530 is light, dynamic, and crisp, sometimes perceived as mild/laid back in energy due to the very clean, short notes that while are dyanmic lack body and weight in the presentation. The Triple.Fi 10 is robust, thick, and energetic which gives an aggressive, enveloping sound, something I describe as "club like." The SE530 is more analytical. The Triple.Fi 10 is more fun. I personally see the Triple.Fi 10 as a better product, and it too can be analytical and balanced if EQing is available.
I haven't used the ER4P but have used the S version. I am not entirely certain how different they sound due to the ohm difference. They are the same drivers but the sound is still apparently slightly different. This is another entirely different product from the two above. The sound stage is very good. the isolation is very good. The notes are thick and well articulated. There's a lot of texture and micro information. Dynamics and energy are a little more subtle but balanced and "appropriate." Being a single BA driver earphone, it is limited somewhat in frequency response. This is unavoidable for a single BA design. Response below 60Hz drops off and response above 12kHz drops off. The quality of sound at the extremes can also be less refined. For the range the ER4 does play, it is very good. The price point of the ER4 is better than the above two as well as you can pick up a pair for nearly half the cost. However, I an still partial to leaning you towards some other, good multi-driver earphones instead simply because there's no way to make up for the lack of response. The ER4 is a product you should own. It may not be a product you'll keep, but it's a product that shows you the meaning of good. It is a reference level product. You will understand the hype and why these remain and remain unchanged even after +15 years. It's just that this is more of a transitional earphone. It's one you buy as your first venture into high end IEMs and go "wow, these are amazing." Then you buy others and find a lot of other amazing earphones as well, and the ER4 remains a benchmark device to compare against. In the end though, the ER4 is just limited as a single BA earphone, and that's all there is to it. It's great but limited.
