Like Steve mentioned, you can convert a 3 phase machine to single phase power fairly easily with a VFD, but a VFD that can handle a 5hp motor isnt going to be cheap, expect to pay anywhere from $300 to $500.
Before you go the powermatic route, id take a step back and ask if your son really needs a 5hp machine. Thats a lot of power for a table saw, and while that may be good in a professional cabinet show where theyre constantly ripping down 12/4 oak boards, but its massive overkill if its only used to cut down 3/4" plywood. Putting aside the cost of the VFD, theres also the problem of power supply and space for a small shop. A 5hp motor requires nearly 4000 watts of power, which would require somewhere in the neighborhood of a 20 amp 230v line. I do also agree, a full sized cabinet saw would take an inordinate amount of space in a one-car garage shop.
Personally, my recommendation would be to pass on the Powermatic, and instead look at getting something closer to a contractor or a hybrid saw. Something like a Delta 36-725 would be my pick, bought new they run about $650 last i checked, and for a hobbiest i think theyre the saw to beat. The built-in mobile base makes moving them easy, the fence is fantastic, and the 1.5hp motor is what i consider the sweet spot for a home shop. Plenty of power to deal with the stuff your average joe is going to cut, but not so overpowered you have to put in a new subpanel to run