If you don't mind "blemished" practice ammo, you can get 50 9mm rounds from Freedom Munitions for $8.99.
9mm 115 gr. RN - B - Blaster Handgun Ammo
Even their brand new stuff is only $9.95 for 50 9mm rounds.
<!02>9mm 115 gr. RN New
Which reminds me... I need to order some more ammo :-D