For 240v I got a 40W Weller one from here for about £17:
http://www.toolshopdirect.co.uk/handtool/brand/Weller
Weller are a good make, and it solders cells etc with ease.
For at the track I have the MRT 12v, apparently it is 40W but doesn't seem so to me, I'd say more like 25W. Not tried it with cells but it's fine for motors and wires etc.
£8 sounds a bargain but you will need a different tip as that says its a pointed one and you will want a flat chisel tip.