I can thoroughly recommend having your own slide scanner along with some decent photo editing software. I have an Epson photo scanner which was very inexpensive but has over a period scanned my entire collection of old slides prints and negatives. The photo software can clean up images, restore them correct exposures, you can crop them - the possibilities are endless and you will have a much better result that suits you than if you sent them off to be done en masse. It takes time but unless you are in a hurry it's time well spent