Timing belt went the mechanic said if head gasket is bent the cost would be too much...he also stated he won't know if head is bent util he fixes belt...what should I do?

I think he meant the head itself. If it's warped then it's a major issue. I'd be more worried about bent valves, that would be the concern. Won't know till you have a look. Hopefully you can just do the belt and be on your way.

Its not the head its the valves that are in the head unless you also had a bad head gasket and it ran hot and warped (bent) head and that is the reason for using these terms. If timing belt breaks it can damage the valves and cam and pistons which in some cases also damage the rods/crank but most times those last two are fine, The head bent/warped and bad head gasket are two different problems that may have happen in short order of time but not connected with each other as far as one caused the other. A timing belt can break and will not blow out the head gasket and most time will not bend the head but can let parts go loose and from head and damage the internal head & head parts. So it sounds like you have it all mixed up as to what happened but either way it either needs repaired or replaced and if its that big of an unknown have it replaced with a known good engine as just the timing belt repair if valves are bent the pistons may have chips or cracks too and just the labour to find out is worth 1/2-3/4 of the total replacement engine alone so I would replace it or the whole car and remember in the future to change the timing belt more often.