There are several sho[s on the web that are giving 1/2 price line rental for about 6 months. But they give you the discount via rebates after about 9 months.

Are there any shops that give you the 1/2 price line rental straight away?

If you are referring to T-Mobile then buy direct from them, and you get their offers discounted on your bill straight away.

All others are promotional offers, and as such, are not direct from the network, so are offered through rebate.

On e2save, all there offers are through rebate. Ill check vodafone and orange directly aswell.