I have a huge collection (over 1000) of 35mm slides that I'm considering digitizing. So far the cheapest I've seen is ScanCafe, at $0.22/slide for large orders, that would be $220 for 1000 slides. I also considered getting a slide scanner, but I don't want to get one where I have to sit there and feed it 4 or 5 slides at a time, it would take years to get through them all. There are very few automated slide scanners that would take either a slide carousel or a stack of slides, and they all seem to be very expensive, with poor reviews (they get jammed, eat slides, etc)
I have used ScanCafe in the past with much success. What they used to do was charge for a minimum of 50% of your exposures. You get a chance to review online and they batch everything. It really comes down to how much your time is worth.
For me, ScanCafe was worth it!
You could purchase a Reflecta Digitdia 4000, 5000 or 6000. This is essentially a slide projector with a scanner instead of a projector lamp. The advantage here is that you can load your trays and it will just scan them all for you. I have no first hand use of this but it is something I want to do myself as I have about 3000 slides and am a bit of a luddite. They also sell very well on ebay second hand, not sure how easy they are to track down if you in N. America but plenty online in Europe. ebay link The other thing is that it has built in ICE for scratch reduction and some are bundled with silverfast aiStudio and also an ITU-8 target for calibrating the scanner so your colours are accurate which is important (the targets are film specific which increases the costs unfortunately).
I have a Nikon Coolscan - 4000 dpi - Film scanner. I paid about $400 for it new a few years ago, they seem to be going for two or three times that used these days.
As @dvar fears, its a slow process. I have a couple of thousand slides that I took with my Nikon F back in the film days. I've started processing, and I think I've completed about 100 or so. It takes forever.
For software, I tried both SilverScan and VueScan, and I like VueScan better.
I don't know if you can rent a scanner, but I bet that 22 cents times 1000 slides is cheaper than you can buy a decent consumer scanner.