I asked a similar question in
this thread, but I am just now getting around to sorting through my slides. Doing a bit more research, it looks like most photographers recommend getting scans done @ 4,000 dpi and saved as TIFF files. This is approximately 65 MB per scan (though I've read some say their scans were about 105 MB). The going rate from respectable vendors ranges from $0.62-1.89 per slide. Here are a couple sites that I have not used but have seen recommended elsewhere. Do your homework.
http://www.slidescanning.com/http://www.saugus.net/Photos/scanning.shtmlFor the volume you have, buying a scanner and doing it yourself is the advice I've seen given most by other photographers. The Nikon Coolscan models are also the only recommendations I've seen. The
Nikon Super Coolscan 5000 ED is the lowest cost Nikon model, and the
9000 the high end model. Unfortunately, the low-cost Coolscan V ED was recently discontinued. Not sure if ebay is a good place to find a used unit, but used units keep their value well. Buy a scanner new and sell it when your project is done and you'll likely not be out much cash.
Personally, I'm not finding that many slides that I need in a hi-rez format, so I will likely use a vendor for scanning some of my slides. I may settle for high quality jpegs for many of my photos simply to have them in a digital format that I can email to family or post on the web. However, if you only want to do it once and do it right, and have more time than money, learning to do it yourself ensures that you get the scans to look the way you want them to.