How can I fix this myself??

I have a 1996 Dodge Caravan recently my heater stopped putting out heat
I replaced the thermostat, checked the heater lines (hot going into the firewall, and even tried to replacing the control pannel (with all the solid state stuff) still no heat.
a specialist tells me that perhaps the solonoid or motor controling the door that opens to let in the heat may need to be replaced to the tune of $600 smackers!! WOW that really hurts! and I am not sure if its worth it.. IS their any "trick" I can try to get some heat without paying an arm and a leg?

I have a 1996 Dodge Caravan recently my heater stopped putting out heat
I replaced the thermostat, checked the heater lines (hot going into the firewall

DId you happen to check the return line coming out of the firewall?
I had a sumular problem on a Blazer, back flushed the core, ran the motor on an uphill incline with the radiater cap open to flush out any air pockets and got plenty of heat. If you remove the lines slit the ends with a razor blade rather than yanking on them.
It's possible that their isn't much water going through the core, but if the line is hot then the door is most likely the problem.