Wanted: Sub £500 Road Bike

you'd need to change the chainset to a double of your choice, the STI levers would work the same, although the LH one wouldn't need so many clicks as with the triple.

I could split the bike if needed, as I'd use the parts on another frame

The alternative is swop 105 double kit from the Giant, or have it resprayed @ £80 and it still wouldn't cost £500

Have you got a link to the Giants actual model?

Would it be worth building it? Surely it would be cheaper that way and I could put on the parts I actually want.