To the OP the RS-1 are fine headphones and are one of the best Grado's made, however people may rightfully disagree as well. To me they are a worthy upgrade to the SR225 and a definite improvement to the SR325is and SR325i. I dont think getting a RS1 used for that price you are looking for is a good deal, especially if you get taxed for it and not to mention possibly loss in transit.
Like others have mentioned a good alternative option is getting a pair of HF-2. If you look around you will find it is constructed using aluminium and wood like the PS1000 thus some think of it as the "baby PS1000" It has also argued if they reuse SR325 drivers but despite this uncertentiy they do not sound like the SR325 and any of the SR325 variants made. I wont go into details about how they sound but if you search for it here you will find endless amounts of impressions for them.
What I would do is skip the RA-1 and grab a HF-2. The RA-1 like others mention seems to be not such a great deal for the cash. Just to give you an idea I have owned the RA-1, and I currently own the following HP-1, HP-2, RS-1, RS-2, HF-1, HF-2, Grado SR325 Magnum, and SR325 (Joe grado HP1000 drivers in them) and have owned SR60, SR80, SR125, SR325is and SR225 and I can say the HF-2 is something special because of what it offers at that price level and it is no slouch compared to the RS-1 either.
About amping i find that while RS-1 and HF-2 are better amped but I dont find it such a huge improvement as they were build to be easy to drive. I would instead like to instead recommend getting a better source or some kind of DAC such as a pico or a gamma 2. If you are do decide ever decide to go with a gamma let me know as I will have one for sale soon due to upgrading to a buffalo 32 dac, and will be traveling to the UK and could just bring it over and mail it there. If you also would like I could pick up and RS-1 and bring it with my to the UK and I will send it to you domestically to avoid extra charges. Of course that is if you are willing to trust me on this is up to you.