Alright mate, had a similar problem last month with my 05 wrx. The caliper pistons are chrome plated, after a while they can corrode and they start to stick.
To do the job properly you need new pistons and seals which is fine but will cost approximately £100 - this is for stainless steel pistons and all the seals etc.
However, for £200 you can get your calipers professional refurbed and ready to fit - this is the option I chose and the quality is excellent.
Godspeed have a good name but I found them difficult to get hold of (no reply to email or phone) - probably just unlucky.
I decided to use Scooby Worx - £350 up front then refund of £150 when you send them your old calipers. Service and quality was excellent and importantly they refunded my £150 with no problems.
Would definitely recommend them.
Whatever you decide best of luck.
Cheers
Ross.