If you can't get the 580, then the highest hp CUT you can go with. Anything smaller and it will just take time. I built a house from the bare ground up.... Did the site work, footers, utility trenches, full septic system, everything.....all with a 25 hp subcompact TLB (LS MT125)(about $20K brand new now). I was not in a rush, doing a couple hours after work and full days when off.
I sold that LS SCUT, and bought another 25hp TLB, an LS XG3025, which is now called the MT225E, but a CUT size. Even though it is still only 25hp, it works about double what the smaller one could do time wise.
You can get a capable CUT, new with the BH, like the Kioti CK2610, Branson 2515, LS MT225E, etc for about $27-30K with the backhoe. Once you get up to the 35-40 hp units, probably around the $40K mark.
Good luck with your search and projects!