I'd go with a Marauder and tank setup. If you're in Florida there'll be plenty of scuba shops around to fill a tank for you. You can pick up a used tank for < $100 that'll fill your rifle around 80 times, and depending on the caliber, get you 24 to 50 shots per fill. The smaller calibers use less air per shot and generally are a bit quieter. I love my .25 Marauder, hits hard and very accurate. I don't know how hard lizards are to kill so not sure you need a .25?.
Good idea on the tank, although I think you would want to go with a SCBA tank that is 4500 psi vs 3000 for scuba.I get about 20 shots with my .25 before I pump-figure 4-5 pumps for each shot,so if I shoot 20 I plan on 100 strokes on the pump.Great exercise.
