car door lock faulty?

i have a renault clio rt 1999 plate and the back door lock has jammed down on one side. won't force up and central locking won't open this one door. lock seems to be resisting when pulling up from inside. tried to take the door panel off but seems to be glued or something as when all seals taken out was still tight to the door. any ideas on a quick fix, or ideas on kind of price to get repaired??? not sure if some one pushed down on the inside but the latch only goes down as far as the other back door