"an opening for a bar fridge" Does that mean it needs to be short? Under the bar? Shelves above it? Most cheap apartment fridges can be modified for three cornies, but might be too tall.
I can fit two cornies and my & 7 gallon conical (I could replace the conical with two more cornies if I wanted to) in my 18.1 cubic foot Whirlpool (30" x 66" on the outside) with a wooden platform on the bottom to get past the angled compressor area. The only problem is serving and fermenting at the same temp. (something I can live with).