www.wiggle.co.uk is good for all cycling stuff. Their cheapest lycra shorts for men are £16 at the moment and their cheapest padded undershorts (for wearing underneath 'normal' clothing) are £10. They also have road inner tubes on the 'Sale' tabbed page for £2 at the moment. If you do use
Wiggle, always pick their 'non priority' dispatch option when you check out (the default one is 24 hours and costs money). That way you wont get stung with any P&P charges - it's totally free and it only takes 2 or 3 days maximum to receive your purchases anyway, as long as they have them in stock. Look at the 'sale' page and also browse through clothing and/or bike parts for any other reduced stuff. You'll find you wont need to buy many things at full price on Wiggle.