I have a very old $200+ Rollei slide projector.
To me most important is to get one with autofocus. You have to manually focus the first slide and the projector will automatically focus when changing slides.
This is because most paper/plastic mount slides are not of the same thickness, when the slide get change it may not locate in the same focus plan as the previous slide. Some time when you view a slide for too long, the heat of the lamp may cause it to warp and thus out of focus. In these cases the autofocus is very usefull.
As for bluring at the edge, you need to place the projector at a minimum distance away from the screen, depending of the lense you have. If use correctly a $200+ projector can also produce good result.
The principle is that the slide projector is a point light source, the distance from the centre of the screen to the projector is not the same as that measure between the edge of the screen and the projector. If the projector is place futher away from the screen, the difference will be quite small.
A slide projector is a simple piece of equipment, unless you want to have fancifull feature like fade-in fade-out, or be able to trigger by tape signal or syn with a few projector. It is not necessary to invest in Kodak projector which are quite expensive due to its expansibility options.