when we stayed there in April, wifi was 100baht for 48 hours unlimited
That is 48 hours from the minute you sign on, they have wireless modem on every floor so no problem with reception, and have also 2 pc's in reception which you can use with the same card.
And the guest house is a stones throw from THE KAFE where all the GT guys hang out, also undercover parking for your bike.
Boonthavon Court http://www.boonthavon.com/
straight across the street from Ban Wiang is also ok.
At either of these places, you're only 150 metres from the Kafe & Mr(s) Mechanic, so they are highly recommended. Both also have under cover parking. The renowned Dr G stays at the Boonthavon, as does Bomb Defuzer, whilst Jimoi & Tropical John use Ban Wiang. Take your pick.