Yeah, practicing shooting from various positions is definitely a Good Thing. Dry firing is a Good Thing, as well. The better you can coordinate the sight-picture and your movement of your trigger-ginger, the better.
I don't care what the store charges, ammo is cheap. Look at it this way: You have umpteen hundred dollars in the rifle, scope and hunting license/lease, whatever. There are the trip expenses. Add it all up, and compare it to a couple or three boxes of ammo at even $20/box. Ammo's cheap.
And don't psych yourself up about Bambi. A datgummed deer ain't nothin' but a goat's cousin, with funny horns. Goats smell bad. Just focus on that basketball, and forget the rest of it. You can "Ooh!" and "Aahhh!" after you gut him out.