What do oyu think a back street garage would charge to replace head gasket on a 2006 mk2 ford focus sport 1.8 TDCI engine ?

11 months ago I notice the water in the bottle was dropping a bit, found no leaks so got a chemical test done, changed color and was told the head gasket had failed. however a garage diagnosed and charged for that job last year but we don't know if it was actually replaced and if they conned us but maybe the test picked up on that ?

I've done approx. 20,000 miles without much problems though related to HG and still drivers GREAT

Anyway, my car doesn't drive like it has a head gasket fault, no smoke whatsoever, even in freezing conditions, no power loss ( in fact the power is amazing and car is very fast) no oil/water mixing.

However the top radiator hose feels harder than it should be ( cap holds 21 psi) I have had about 4 or 5 water leaks from hoses and pipes and the radiator blew and I had to replace that too. also when taking cap off there is a lot of pressure in the bottle when taking cap off.

Just wondering, if the head gasket is gone and I decide to get it replaced at a back street garage how much do you think they will charge ? ( this car has had over £2,000 spent on since last year, also needs other things that can be left but if the hg is replaced may as well sort them too, or just drive the car as it is for longer and sell spares or repair or something )

car is a 2006 ford focus sport 1.8 tdci with 153,500 miles on it.

edit:  in case I decide to not have the HG replaced then I would like to know, could I get another rad cap with a lower psi ( 21 currently) to fit on my car to lower pressure to prevent any further possible leaks/blown hoses ? )

also when should my belt need to be changed , was supposed to have been replaced at 126,000 but don't know for sure but it was definitely done at 95,000.   in other words how long can I keep driving with current belt if it was replaced at 95,000 and then  can you tell me also at at 126,000 ??

thanks