Quote for installation of unvented cylinder and associated works

Hi folks
My cottage has no cold water tank or boiler. I'm on E7 so my only means of heating water while on cheap rate is to fill up several 5 litre flasks every morning!
I have received a quote for installation of a 90 litre mains pressured unvented hot water cylinder.
It will be sited in the understairs cupboard on the ground floor - which is a central point in my tiny cottage.
The quote includes installation of a Horstman Economy 7 programmer, pipework to the bathroom (ground floor) and to the kitchen (ground floor), installation of a new mixer shower in the bathroom (to replace current electric shower), hot and cold pipework to the kitchen sink and new taps to the bathroom washbasin (which currently just has a cold tap). Plus electrics of course.
I've no idea why they quoted for a 90 litre cylinder - we discussed 60/70litre though I don't suppose it will make a huge difference to the quote which is around £3,250 plus vat. :eek:
Anyone have a clue if this is reasonable?
Cheers