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If you want to reconsider doing it yourself you can greatly reduce the time factor if you get one designed for doing many photos at once. I'm pretty sure they have self fedding ones and/or one that you may have to manually feed the images instead of opening and closing the scanner top all the time. I'd also make sure it had digital ice or similar technology, digital ice is special type of defect removal system. It scans for physical defects such as dust and scratches and will automatically remove them. Since its looking for physical defects on the surface of the photo it works very well. It's not a software based system like noise removal filters you would have in image applications.
If you're doing this for archives I'd suggest making sure they are scanning them at high resloution. Preferably saved in lossless format like .tiff. 300 DPI minimum for a 4x6, that should be about 1200x1800 pixel image. Secondly see if they are using the technology or similar I mentioned, anyboby can batch process a bunch of images using software filters but its not nearly as good as the hardware where fine details are concerned. Software doesn't know if it freckles on kids face or dust...
Do you happen to have the negatives? You'll get better results getting them scanned.