I've still got my trusty old Nikon projector from the 70's. This uses the "universal" trays (either straight or rotary) that also fit Sawyer, GAF, Vivitar, etc. IIRC it's basically a spiffed up Sawyer but with a superior Nikor lens.
I'll have to check when I get home but I believe the Carousel trays also work in my Nikon. One advantage of the "non-Carousel" projecters is that they also take the straight trays for small batches.
Make sure you get one with a zoom lens. Stack loader is also handy, although most occasionally jam. Autofocus is also nice as many slides pop as they heat up and need refocusing.