I was at Ax-man Surplus in St. Paul yesterday and saw what might have been the perfect lagering fridge. I don’t know a whole lot about it, but it was a VWR Scientific mini-fridge with a digital temperature control. It’s one of those ~4 cu. ft. models, not sure if the compressor “shelf” would make it too small, looks to me like there’s a pretty solid chance a carboy would fit in perfectly, though. There’s 2 there $95 each. Might be worth checking out.