I think the structure of the 3-5-7.5HP models of that saw are all the same. Swapping the motor is probably the safest/cheapest way and I suspect
your are out about $300 or less. If you check the price of a single 5hp with them it might be only a little more and you might find that a better option, JMHO.
I was looking at a 3 phase Sawstop a few years ago and contacted the company regarding using a vfd and was told that they have had many reports of the machines not working well due to all the electronics in the machine. I was quoted the electrical parts as well as a 5hp motor for it for a couple hundred dollars. I was very surprised, it may not be as expensive as you think.
Where are you located? I might trade you a3 HP 1PH of close to the same vintage...
I know this is an old thread but I’ve got the same situation as the OP.
What’re the chances of finding someone wanting to convert to 3 phase?
Probably very small. Some good advice in this thread. The one that caught my eye was “I was quoted the electrical parts as well as a 5hp motor for it for a couple hundred dollars.” I’d pursue that option first.