Good idea, comrade...
The 3 to 4000 baht bracket are mainly family hotels, often not GF and so you'd have to ask to be sure.
IMO, your best bet is one of the hotels on the Beach Road between Karon Circle and the Hilton, like the Baan Karonburi or the Karon Princess.
Straight across the road to the beach, easy to walk to Karon, which with a tuk tuk minimum of 200 baht has to be a factor.
The Thavorn Palm always has a lot of Russians, but but it is nearer to Kata than Karon.
Threre are also some quite well positioned hotels on the Patong side of Karon Circle. Again they are family hotels, Best Western and the like, so you need to ask.
The Pacific is highly rated on Trip Advisor, the owner spends a lot of time making sure it ranks high, and is an OK hotel, but is not within comfortable walking distance of the beach or the bars.
The best hotel in Karon itself is the Centara Resort, which may or may not be GF, depending on who you ask. I've certainly seen plenty of girls go there from the bar soi and not have a problem, though I've never stayed there myself.
However it's a bit more expensive, though you may get an early deal.
The Sugar Palm, also right in Karon, requires girls to check in at the same time as you or a joiner is charged, in my experience.