There is a joint on the wires going to blower motor that tends to give up. Check that and the connector itself to the motor is known to get sparky. Try to get the motor out and you will see what i mean or just wiggle the connector on the motor with blower and ignition switches to ON position.
For radiator, $500 sounds too high to me. The new radiator shouldn't be more then $200 and its fairly easy to throw it in. So, If you are ready to get your hands little dirty for the sake of your bank balance. Do it yourself, This forum is always there to help you at any stage.

 

^^^ true.

we are always here to help. if you do end up doing the work your self i can PM you my cell number if it would be of help.

 

here is an awesome write up if you are interested in what its gonna take

https://volvoforums.com/forum/volvo-850-16/1997-volvo-850-non-turbo-automatic-radiator-write-up-30589/

 

i wouldnt use a rad. sealer.i agree with tony850 look to see where the leak is coming from.could be just a hose.RULE #2 when going to a shop.dont look clueless.if you know what is wrong research it a bit.you will get milked.i understand you are a novice but the rad. is not too hard of a job.just time consuming.