I have a Micromark MM40061 wireless alarm that was originally from Argos but being lazy I never got around to fitting it! Was about £100 IIRC.
1 x Dual Power Control Panel/Siren (solar panel/battery)
3 x wireless PIR sensors
1 x wirefree door/window sensors
Also has a remote keyfob and comes with all batterys.
Is brand new and boxed (has been opened), would do for £40 delivered.
PPG or BT.