Once you evaluate what your costs are domestically, my strong advice is to give consideration to seeking out reputable dental clinics abroad. I recently started treatment for a couple of dental implants (plus a root canal and various neglected cavities needing fillings) I need in Thailand, at a clinic that caters to about 90% foreigners (and the rest wealthy locals). All told, the estimated cost to get the work done in the US was going to be between $15-20K. The cost to have it handled in three trips to Thailand, including flight costs from the west coast, hotels, and food, is looking like it will be about $7.5K. While I was pricing that, I was looking at options for my fiance's dad, who is in a very similar situation to your dad. My quick numbers suggested that for what he would pay in the US, he could have an all-on-four or all-on-six implant dentures done over there, including all his travel costs. This would be a permanently installed fixture, rather than the archaic dentures. Alternately, he/you could just save a huge amount on traditional dentures.
Just something to think about. I am working on a series of posts about this (blog link in my signature, it's a subheading under "Thrifty Travel") and have chronicled my experience so far, but it has been extremely good. The biggest reason aside from the huge savings is that the kindness and high level of compassion I experienced was just what I needed after a lifetime of judgmental and unhelpful dentists in the US. I am very fearful about the dentist and know well how it is to have your confidence and wallet challenged by dental issues. If you have any questions at all about this kind of thing or my experience, please feel free to PM me.