The cost for materials and labour varies, it will depend on the supplier, and the labour rate for those doing the work in your part of the world.
 
Front easy to do yourself, but rear needs welding so 200gbp sounds right ball park given the tops are about 45gbp each to buy.
 
If it is rear and they are rusted out, then also plan to have the rear chassis fixed , as they tend to go in the chassis behind the damper bracket and the spring mounts. Look OK, until you give them a poke, then Ooops.

Cheers
 

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