I built my own 5-liter system out of used Heineken mini-kegs and a bicycle tire valve a few years ago, but I don't use it anymore. Website with pictures showing how all this was done seems to be down at the moment, if it comes back remind me later and I'll provide a link. If I were to do this today, shoot... I think I still might even ask Santa for a uKeg this Christmas. But yes, they are way too expensive really. Your best shot honestly is probably just a standard growler or two, kept in a cooler with some ice packs. That's pretty standard, albeit unluxurious or showy.
EDIT: Aha, here's my link: