How much for gas combi boiler and heating? read on..?

I'm mid terrace and i just got a quote to remove existing heaters, hot water tank and cylinder, install a 28i boiler with vertical flue going out my roof (so need a roofer too), gas taken from cupboard by front door upstairs to boiler (old water tank cupboard), 3 radiators (living room bedroom bathroom). Anyone done the same? How much? I'm going to get more quotes but not for a while since it's easter. Also any idea how much cheaper it'd be getting the boiler in my kitchen rather than cupboard upstairs so not thru roof for flue??