Wanted: Shimano/sram 10 spd groupset

Check Ribble - good deals on Shimano components

I've done up an MBK Mirage Pro here using 105 5600 parts from Wiggle.
http://www.lfgss.com/thread81615.html

105 5600 double chainset = £60
Matching BB = £15
105 5700 10sp Cassette = £30
105 5700 Chain = £17
105 5700 Rear Mech = £30
105 5700 Front Mech = £19
105 5600 10 speed lever + cables = £128
105 5700 brakeset = £52

Grand total for your brand new 105 groupset = £351

You can always get second hand shifters for about £75 on eBay to stay within your £300 budget.