If you are at all considering tubes, the Mapletree Audio Designs Ear+ is outstanding with low impedence cans like Grados.
The Ear+ (basic) kit is $295. The website for MAD is
here The Ear+ basic is the same sonically as the Ear+, just doesn't have the wood side panels.
Or, if your going the DIY (or DIYFSOE) route, could consider the RA1 clone (maybe $30 - $50 or more in parts, depending on your case), a CHA47 (maybe $30-$60 in parts, depending on your case, META42 (from ~ $100 - > $300 in parts, dpending on your case and how exotic you wnat to go) or a Gilmore "Lite". I believe the Gilmore lite was going for $295 assembled.
All of these amps will sound very good with Grados. Do a search for reviews.
If you are at all interested in DIY, would make a lot of sense to try out the RA1 clone. It's a modiifed CMOY amp. The CMOY is THE beginner amp that folks suggest that you start with. You can get excellent documentation on building a CMOY at
Tangents site.
The CHA47 is also a great amp to pair with Grados and it's pretty cheap to build, but sounds very, very good. Or you can contact one of the DIY gurus here (I know JMT is still building these.. not sure about KurtW or Tangent or others) to build one for you for a very modest price.
Good luck!
Bruce