Undervalued? Hmmmm, this is certainly an arguable choice--but what about the Nikon F4?
I mean, nowadays you can easily get one in nice shape for under $300. And yet when it was released, it was possibly the best and most revolutionary camera in the world--with a price to match.
Yes, it is big and heavy--but not really much if any heavier than a DSLR. And it has the advantage of having a far better viewfinder--you can actually manually focus with it (after using a DSLR for a while, when switching back to the F4 it's like looking at a movie screen, it seems so big, bright, and clear)--plus a metering system that is 99% as accurate as anything out there today. And it will work with most of the lenses Nikon made throughout its history--it will even autofocus the G lenses, if you don't mind shooting them wide-open.
Can I go back to that viewfinder for a second? Interchangeable screens (and interchangeable finders), built-in diopter adjustment (and will take screw-in diopters for even more range and fine-tuning), focus indicator, a great meter showing you exactly what your exposure is for +/- two stops, shutter speed, aperture, and number of exposures visible, convenient switch to keep it lighted. Everything you *need* to see, right where it needs to be, and nothing at all to clutter it up. And you can even take the finder off if you want to shoot discreetly at waist level--and you'll still have spot metering at least. God I *wish* any digital camera made since had a viewfinder like that! Shooting macro was especially a fun experience with the F4--and my slides, whether shooting daylight or flash, were almost always perfectly exposed.
You can get one even cheaper than many crappy plastic point and shoots, and it will be much more durable, accurate and capable, and you can mount some of the finest classic glass ever made on the front of it. And firing it just *sounds* brilliant, too--I think most movie camera firing/motor drive sound effects were based off the F4, seems like.
It's just damn fun to shoot. And possibly the best bang-for-buck available today in the film world.