We used a local place here that did a terrific job, but they weren't cheap We had my DH's parents honeymoon from the 1940's on reg 8 mm movie film, and they transferred amazingly well, also some of our older DD on super 8 film. They added some light music background, as of course there was no sound. You would do well to get a locally owned place, if possible, and see some of their finlshed work. Good luck! We have not tried doing any of our slides yet.
I sent 1000 plus slides plus 8 reels of 8mm film. I bought a few groupons for the company (I could stack them). the quality was great, just a bit slow. But these slides and reels were sitting in boxes for 30+ years, so no worries.
Sams Club* will transfer slides to a DVD on site and it cost .17 per slide and the. The cost of the DVD which is 3.96 and they also do the 8mm to DVD through YesVideo