Hi, you have to check with the manual to find the maxium amount of ram it can take. The for the hard drive, you have to find the type of hard drive (probably ata). This can go up to any size.
You may have a little problem getting the OS back on, but I wouldnt think it would be too bad for just the ram and hard drive.
Typically I look at
www.newegg.com for prices but just shop around to get the idea. Prices are based on the size and type of everything you get.