Coolant leak

I have an 87 chevy celebrity 2.8 / v6 250,000 on it and I getting coolant in the car on the passenger side floor I was told it was a heater core leak. Now the thermostat is reading hot and the rad is cool to the touch. I have been filling it with coolant regulary and the thermostat has never read hot. So, is it my my heater core thermostat or is there more than one problem?

I was also told it could be a head gasket. Is ther a way to check for these problems or should I just take it to a machanic?

i only paid $500 for the car should I scrape it?