Older used gaming computer VS new budget gaming computer help

Hey guys so i have a question, me and my friends have started playing rift and one of my friends has an old acer computer with an ATI radeon hd 3650 in it. It does not fair well with rift around 20 FPS on lowest. So he is going to buy a used computer off of someone on kijiji (Canadian version of craigs list) for $450 the specs are:
Processor: 2.4ghz Q6600 Quad Core
Ram: 8GB Gskill PC-8000 ram
HD: Samsung 750gb hard drive.
Graphics: XFX 9800GTX+ graphics card 512mb ram
OS: windows 7 ultimate edition
Also it is made by a company called shuttle it is a very small case, looks like it would be used for lan partys or something. Anyways my question is, is it good for him to buy an already outdated computer or spend like $500 and build a budget build? It has to run rift well on medium-high. Thanks guys