hi mate,
lowering the car 25mm or so will make a bit of a difference, any lowering springs will. it won't look "lowered" though if its got the massive tractor stance that most standard cars have when you put new wheels on, but it will bring it back to reasonable.
as for buying some, i've got some 'cos i fitted coilovers to mine. im in north yorkshire and would let mine go for £70, so £30 for petrol from cheshire and bob's your uncle.
it may increase your premium, it really depends on who you're with etc. cant guarantee either way, you'd have to ring your insurers and ask them.