Jostby, you're right, like most things, scanners included, you get what you pay for, the key is determining what quality of scan that you actually need.
To be honest I don't think there are many decent scanners for much less than $500 (new $150 -$200 used on ebay). At least if you want to get adequate dynamic range, the ability to show details in the shadows and the highlight areas in your scans. So unless you?re willing to make that kind of investment you might want to have them done by somebody else until you can determine what quality of scan you need.
I literally have 10s of thousands of negatives and transparencies that I'd love to have a digital copies of but the reality of it is only about 10% of them are even worthy of being considered "scan worthy" so I would recommend that you cull out the ones that you don?t need as there not worth the time, or money, to scan.
I?m not sure about the cost of having it done by another party (Walmart, Ritz Camera etc) as I do them myself, I currently have a Epson V750 Pro / $800, but I have found that investing in a small portable light table (mine is about 11?X14? $50) and a good viewing loupe ($20-$50) is the key so you can edit out the bad images, this ultimately saves a lot of time and is especially helpful if you are paying to have them scanned.
If your not used to reading a negative through a loupe it doesn?t take long to figure out what to look for (is it a least in focus) before even considering having it scanned.
Once I?ve picked out the winners I then mount the selected negative into a 35mm slide mount were you have to cut the negative down to the one frame (a box of 100 Pako plastic slide mounts is roughly $7) this helps protect the original negative for long term storage and makes them easier to handle. It also gives you a surface to write information on about the image. If you go this route you need to invest in a pair of cotton gloves ($5) to keep from touching the negative / slide surface with your bare hands.
Before even considering a scanner I would highly recommend that you have a couple hundred of them scanned professionally and see if that meets your needs before making an investment in a good scanner. I used to get this done in 12MB files (more than adequate for making 16X20 prints) for 20 cents. If you do the math, at 20 cents a scan, you could get 2500 images scanned professionally for $500.
The other thing to consider is the amount of time it takes to scan an image on your own, my experience is that you?re lucky to get 15-20 scans done in an hour which obviously is going to get time consuming if you want to do even 1000.
Steve