5 hours at £50 an hour = £250
Or
Materials at about £100 all in (leather, glue, sewing machine, new needles, brush's cotton thread, electricity, lightbulbs, heating etc etc.)
£3 hours at £50 - £150 (to include national insurance, pension, tax etc....) inc removal and fitting...
£250 seems reasonable to me!
Have they got examples of prior work and have they seen the Zed ones? Normally the door cards these guys do are flat... the zed ones are far from it!