Actually, there are a handful of CD/DVD changers on the market that hold hundreds of discs and are expressly made to hook up to a PC. The one I used is called the PoweFile C200. It hold 200 CDs or DVD's and has a robotic setup inside to mount any of the discs to one of two internal DVD drives for reading to the PC. New, these kinds of changers average about $4-6000.00 (US), but can often be had on eBay for about $600 if you don't mind getting them used.
Alternatively, there are companies out there whose sole purpose is to rip massive amounts of CDs to MP3 for you so that you don't have to do it. They average about $1 per CD, but it's supposedly convenient and you get them back inside a week or so.
Hope this helps,