Most of the processing labs use similar technologies for their "scans". They use the same device for making prints from negatives. The "scan" is a digital photo of the negative that is then processed and written to CD. Usually this is done with default settings for exposure, contrast, color balance, sharpening, and grain reduction. The usual result are large files with poor resolution and tons of artifact.
You can have a custom scan done, but expect the price to be relative to the time it takes to create it ($$$).
The most cost-effective route is with one of the better flatbed scanners or a mid-range dedicated film scanner. The entry ticket is about $200 USD with the value point being somewhat higher than that.
As for what I use:
- Nikon Super Coolscan 5000 ED for 35mm
- Epson V700 for medium and large format
I have used the V700 for 35mm, but the negatives must be FLAT to get good results. When properly dialed in, the V700 provides a good clean 2400 dpi and the appearance of somewhat more with judicious application of sharpening.
Steve