Training courses are an investment, not a cost.
To further explain:
Once you go to a class, you will have a solid foundation in which to conduct further practice (range sessions/dry-fire/etc).
After taking a good class, your range sessions will have structure and purpose, thus, you'll shoot less ammo and waste no time.
Those two factors alone, will reduce your costs.
BOTTOM LINE:
I was once a "poor college student" and understand your situation. However, being poor is no excuse.
Save your pennies (you know where the extra money is leaking to: women/beer/etc). Find the closest one-day carbine class in your area and start saving for that class. Temporarily eliminate that 'frivolous leakage' and before you know it, you'll have the cash you need.
Ammo, eye/ear-pro, some magazines, and, an open mind are all you need to take that first formal training class. These things are attainable, even for 'poor college students.'
You have to make it a priority, otherwise, it won't happen.