try and buy from the same place, you'll have slightly less issues with returns, and often scan and the others have slightly cheaper bundles you can take advantage of.
Do you have any parts you can reuse?
Aria are currently listing the i5-2400 at 149.99, scan is at 148.98, both on pre-order.
Scan currently have the 2500K for 153.59 (today only offer Expires monday 14:00ish) for the extra it is worth it, if only so that in a while you can upgrade the mobo to one that can overclock.
I know you are on a budget but you are so close to getting something a lot better, can you wait for a month and save up another £50? cut some grass (the legal kind).
Also for a real budget build AMD are cheaper. Look at the $500 SMb build posted on friday.