The 17HMR and 22Mag both are good rimfire choices if your shooting out to 100yards with your practice rifle.
Have you considered a 223 for this though? Very cheap to shoot, and if you reload you'll find you can really stretch a pound of powder out with it. Or even for that matter a 22Hornet. Factory ammo for it is very expensive, but if you reload for it, it doesn't eat much powder at all.
Pick up some cheap Remington Bulk bullets and your in business.
Just a thought.
-Aaron