I have the WRT610n, a little more than your budget allows at around £100 but it's a brilliant bit of kit, especially with DD-WRT installed
Have you tried DD-WRT on your 615?
I have a Netgear WNR3500
It's dual band, has GigE ports and has worked faultlessly over the last 6 months. Nice and easy to set up too.
Avoid Edimax.