Hi,
As above, we work it out on an hourly basis internally, but put the price on the quotation as an 'all in' cost. If asked, we provide a breakdown - man hours/supplies/insurance/etc/etc . .. . but don't make it our policy to provide this unless they ask.
As the job progresses, you get more efficient, so this method of quoting ensures you benefit from this increased efficiency.
As for £25/hr . . . well, we can get away with about half of that down here in Dorset. If you feel it's acceptable & achievable, go for it . .. you'll soon get an answer from your prospective customer that will tell you all you need to know.
There's nothing wrong, by the way, in asking your customer what their budget is. That way you don't price yourself out of it by being greedy, whilst it also enables you to judge on whether it's worth entering the race to start with.
Good luck.