4GB for this board will cost you $100 on average.
http://www.memoryexpress.com/Products/MX41429
This isn't even DDR2, or DDR3
Kijiji:
Acer desk top - Saint John Computers For Sale - Kijiji Saint John Canada.
And yes, it's a few years older, but much faster. You can probably replace the MB, Processor, and RAM for a better one at a store for under $250 new parts.
If someone else is willing to part with them cheaper, keep looking.