I have a 15 hp briggs motor on a craftsman mower. I got it from a friend, free... I found out why... The starter wasn't working, so I replaced it, the carb was junk, so I replaced it. The battery wouldn't take a charge so I replaced it... 225 bucks into it so far, and now it won't even try to start. Im not getting pwer to my starter. I jumped all my safety switches out. No luck. If I put a screwdriver across the two sides of my solenoid, it will start and run. I can try to jump across my key switch and get nothing. How likely is it that the start solenoid is bad?

Sounds as though your solenoid is shot. Replace and you can use an aftermarket for less than $10.00 and an oem briggs solenoid could push $20.00 to $30.00.