I usually charge $100 plus the kit for a complete rebuild. For an Extra 20 I'll give my best guess on jets and metering rods to fit your combo (if it's not the stock carburetor or you've modifyied the motor) An extra 30 will get it mildy modified, an extra 75 will get it modifyied to the hilt (Way past what jet does to theirs) for either off roading or racing. For this bring it by after you've installed it, or buy the beer and have me come over, and I'll dial in the mixture screws and idle included. If I didnt' build the carb for you it's $20 if you just want it running ok, $45 if you want the works (includes reseting timing and such). Total dial in on car/truck can add up to some time, and I'll do it for people, but I charge heavily. To get it dialed in you have to drive the thing, while either having an O2 sensor hooked up and reader (preferably wideband), or keep pulling the plugs, or using something like a g-tech in a pinch. Each time you have to pull the top plate off the carb, make a small change, put it back together and do it all over again. Now after all this the vehicle will run damn near like fuel injection, get better gas mileage and power, but it's a pain in the rear and you should pay for it, plus the cost of jets and metering rods. Can easily add up to couple hundred dollars and considering I'll usually have an extra 4-8 hours in it, thats a good price. Hope this helps you out.
John