Pellet rifle is a great way to stay sharp, but, you also need to train with the firearm you are going to depend on. I use a pellet rifle at home, and, as mentioned, it's not a toy. I have a Ruger .177 pellet rifle that will put a lead pellet out at 1100 FPS and a BPS precision pellet at 1200 FPS. Great practice.
Then, I get out to the range at least once every week. I don't shoot a lot, also shooting .40 S&W, but, generally 20-30 rds, in groups of 3. I shoot at 3 yds., groups of 3 shots, as quickly as I can. The goal is to get 2 or 3 shots off in 2 or 3 seconds into an 8" target. This is a tactical drill. If you have the ability, set up 2 lanes, side by side. Train the same drill, but, side step to the next lane and fire. Then, back to the previous lane. Another tactical drill. The idea is, if you're in a critical defense situation where someone has drawn a firearm on you, the first thing you want to do is maneuver to the side. Avoid being shot, while drawing down on your target. Just one lateral step, then fire. Any hit in the 8 inch "center of mass" target is good. The furthest I'll train with a handgun is 25 yds. Realistically, you're not going to be in a defensive position any further out than that and more likely, much closer. Train for the situation you are most likely to encounter. Make the training count. You don't need to fire 300 rds. at every range visit. 20 or 30 to stay sharp and keep the drills focused. Concentrate more on your posture, draw, stance, extension and rapid acquisition of a center of mass target.
I'm seeing .40 S&W back to around $25 a box here.
EDIT TO ADD: Let me know what you think of that S&W SD40VE. I'll give you my review after you've tried it out.