well since the e280 is 8GB i would say you got a solid price
cause newegg.com currently sells those for about 110 dollars.
i got my e250 (2GB) about 2-3weeks ago for 47 dollars out the door on ebay (newegg wants 69.99+shipping for it new... but main reason i went ebay is cause with newegg there's probably a good chance you will end up with a v2 player). it was refurbished but looks brand new.
as for rockbox working all you have to do is check the firmware version on it by doing this...
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Note: Rockbox doesn’t function on the newer v2 models. They can be identified by checking the Sandisk firmware version number under Settings → Info. The v1 firmware is named 01.xx.xx, while the v2 firmware begins with 03.
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before i ordered mine i asked the seller on ebay a question to make SURE it was a v1
p.s. in my opinion it's just cheaper/all around better to get a smaller initial GB player (say 2-4GB) and then add more to it (if needed) through the MicroSD slot.... and me personally i most likely wont need more than 2GB that i currently have cause im converting all my music to 45kbps .OGG (one of the main reasons i run Rockbox) files which still sound quite good considering the super small file size (you may agree or disagree on that) ... so it's like even though i only have 2GB on my player it's sorta like i have 4GB+ (based on 128kbps .mp3 vs 45kbps .ogg ... 128kbps mp3 is what i consider the minimum before sound quality starts to go out the window with mp3 format... cause between 128 to say 96 or 64 i can clearly tell the difference at that point with my own ears... but one thing is for sure, .ogg is clearly superior to .mp3 at the lower bit rates (i.e. say about 96kbps or lower)) cause i can noticeably tell a audio quality difference between the two.
also in general to get the best audio quality from ogg it's best to go from original audio cd to .ogg instead of something like 192vbr mp3 to ogg