What Is A Reasonable Amount To Pay For Fixtures And Fittings On A House Sale ?

I am looking to buy a house which is on the market at just under 260,000. the sellers have indicated that they are looking for near asking price
i am looking to offer 250,000 + an amount for fixtures and fittings – it is a three bed detached, small third bedroom – what is reasonable to offer for carpets and curtains which are in good condition ?
I don’t want to offer too much and then be told by land registry that the amount was to high and incur extra stamp duty charges .
what have other peope offered when buying their houses ?