I just want a working motion sensor and a working light any ideas how much it would cost

You can buy the lights (8870) and motor (8883) in the normal Lego store
as they are common ‘power functions’ parts.

http://shop.lego.com/en-GB/LEGO-Power-Functions-Light-8870
http://shop.lego.com/en-GB/LEGO-Power-Functions-M-Motor-8883

The special Wedo parts are available in the full kit

9580 Lego Wedo Construction set

or individually as parts

9581 USB hub
9583 motion sensor
9584 tilt sensor

Wedo parts are normally only available from the special ‘educational’ Lego stores e.g.

US:
https://shop.education.lego.com/legoed/en-US/catalog/product.jsp?productId=9581

UK:
http://shop.legoeducation.com/gb/product/lego-usb-hub-9581-54/

but do also sometimes come up for sale on bricklink.com and eBay


And yes, you are not mistaken, the 8883 motor is really offered in the UK at
£5.99 on the Lego consumer store and £10.79 on the Lego education store
- it's exactly the same thing and both are Lego's own stores!