I would recommend a minimum of 16 ga. for this, 15 ga. if possible. I have this 15 ga. Ryobi cordless that I got for less than $150 (the price has apparently increased since I bought mine) , it was allegedly pre owned but looked pretty much new to me. If you go with that you can even get a sander since Ryobi also has a variety of cordless sanders. That is what I recommend, the gun plus 2 4 Ah batteries (which can be had for about $100) would not be much more than some of the kits you listed and you can use those batteries for any other tools made by that brand.