I recently bought a new bike with 10 spd Ultegra. Initially, it came with 53/39 on the front and 12/25 on the back. I already replaced a cassette, so now I have 12/27 on the back. Still, I need more help on hills. My LBS quoted almost $500 worth of parts and labor to replace the crank (they want to replace a lot of other parts too due to compatibility issues).
I hope there should be a better way. Please help.

The cheapest thing you could do is switch out your rear der. with a Shimano XT long cage der, get a new chain and go with an XT 11-34 cassette. Shifting will work just fine, you will get more range on the top and bottom, but each shift will be quite a jump. I would think this could be done for less than $200.

[EDIT] I was just re-reading this thread and noticed you are running 10spd Shimano. My suggestion above is based on a 9 speed cassette/der. This may not work after all... your LBS should be able to advise in more detail.

You could buy a truvativ Roleur Compact Crank for $100. No other parts needed, just need to lower the front D and shorten the chain. No need to go triple as a 34/50 front and a 12/27 rear would be plenty low.

Get the Shimano compact crank. It will work with a standard ultegra derailer.

Agree with capt_phun and primetime_75 no need to change other parts just the crank will do

Everybody, thanks for you help