I'd agree that an ultralight 223 would be a good option for these UT hunts. My brother is down there and will be taking his kids for deer, so a straight pull AR with 77tmk ammo will be high on my list of recommendations. I get about 2750fps with the stand1 77tmk ammo I use in my 16 inch barrel. Stupid accurate considering the low cost of components. Pretty easy to stay under $700 for a straight pull AR15 build, and easy to get under 2.5lbs if you DIY a few things.
Components:
Straight pull side charging upper with half length bolt (like solo300 or DIY)
Portless barrel (like Shaw portless, or get a BCA and plug the port)
Barrel nut (like JAG Composites, or ebay knockoff)
Handguard (DIY, Carbon fiber tube on amazon)
Grip/ti grip screw (like Hogue 15degree or MDT Carbon fiber)
Buffertube stock (like A2 buffertube and farrowtech stock or DIY Carbon Fiber tube)
Lower reciever (like Tennessee Arms Carbon 15 lower)
LPK (like NFA polymer lpk, but replace the grip)
Magazine (like lancer L5)