Nearly every 3-4 room center that was not attached to a major university/academic campus (e.g. UPENN, MGH, Mayo or MD Anderson) has gone bankrupt or had to refinance at least once to stay afloat:
Procure Somerset, NJ
Procure OK City, OK
Procure Seattle
Procure Chicago
Indiana University - shut down permanently
Univ of Maryland - making interest-only payments on their $250 million mortgage, in default
Provision Knoxville
Provision Nashville
Provision Orlando - didn't get done with construction, likely for sale cheap if you want a concrete hole in the ground
California Protons
The one-room centers have been touted as the solution to this problem, but even those are now beginning to fall behind on their repayment terms, including
Proton International at UAB
Proton International at Delray Beach, FL
Regarding the question about private funding for these centers, I don't think debt is a viable model anymore. Interest rates are too high and there is no opportunity to start repayment for at least 2 years - one year for center construction plus one year for machine installation and commissioning. Most of the one-room centers cost about 20-25 million for the building and 20 million for the machine (Varian compact single room gantry or the IBA half gantry.)
There are solutions to the cost problem but I think it requires some disruptive changes and clinical risk taking as far as installing new concepts like the Mevion + Leo Chair system that debuted at ASTRO.