Between a new gas engine, 4 wheel motors, a variable volume pump, adapters, hoses and such, I see 7-8 thousand in repairs in my head, plus the cost of the machine, makes $10K.
Don't know if it's a quick attach or pin-on system. If it's pin-on, there's another $1500-$2K to convert to QA.
Again, those are all severe guesstimates in my head coming in around $12K when it's all said and done. Plus transportation and no value on your time.
Price included two mowers, broom (sounds like a conversion), bucket, forks. There's several thousand in value there. And you could repurpose the Kubota engine that's in it for something, I'm sure, or sell it.
You can get a new PT425 for $16K. But no implements.
You'd have to be project oriented and love to do that kind of work.