They given you a price for a single 2.5" rolled out tail pipe, imo I think that type of tail pipe doesn't suit the
Ibiza. Try getting another price with the tail pipe that you want..... eg, twin 2.5", 3", 4", letter box etc but don't pay no more than the price you got now with the tail pipe you want.
Custom exhuast companies quote you a price depending what mood they in or the 1st set of numbers that comes into their heads. My mate managed to get a cat back system from Longlife in Cardiff for £250 and as he was going out a boy came in asked for just a backbox and they quoted him £200 for one.
There's loads of custom exhuast companies in South Wales, Longlife in Cadiff, another one in Swansea, Prospeed, Z-Ex, Welsh Coast Customs (Powerflow). So just ring around and get some prices.