around £50-£75 mark is what I would charge for that kind of job
depends on how dirty really.
Best way for you to work out your price is look at time it will take to do the job
then multiply by at least your hourly rate.
Allow a little extra time and that should give your price.
i.e. if your hourly rate is £15 and the job would take 3.5 hours
I would charge £15 x 4 hrs= £60
if you are trad then it will mean a bit of elbow grease
with wfp charge the same and the job will be done in half the time