If by "cheap yellow models" you mean the new Venture HC, go for it! My brother and I both just upgraded to the Venture HC. I upgraded my eTrex Legend (blue case, black & white screen), and he upgraded from a Cobra. We got them from Tiger GPS. That seems to be the cheapest place.
The Venture HC is great! It is amazingly fast from boot up, and I get good solid locks on multiple satellites sitting in my living room. With my Legend, I had to set it on the bay window seat to get any satellites at all, sometimes that was iffy, with the accuracy being 150ft or more. Right now, my Venture HC has a solid 8 satellites and my Legend has a tenuous 3. My Legend always had trouble in trees. It would jump around, and sometimes simply refuse to update position until I got to lighter leaf cover. Yesterday we were out in some horrendously dense trees and brush, and never had any trouble with the GPSs.
The screen is very good; high resolution, clear, sharp, easy to read. Although it is physically smaller than my Legend screen, the increased resolution more than makes up for it.
The Venture HC is also extremely configurable, to the point of confusion at times. I assume you're handing these out to novices, so I would suggest that you limit the screens that are available via the "next page" button and reconfigure the data fields that show up on them.
If you (or anyone else) have any questions, please don't hesitate to send me a message.