Need Suggession for Billing Logic

I need your suggestion in billing logic. I have two options for billing
1 ) Use Database
2 ) Simple Files

I’m in the favor of using option # 2 as in this case, load over system will remain low while on the other hand, i must have to open a new connection in the SIP channel to make sure weather the balance is available for a particular call or not and opening a new connection at every new call will make my system slow in performance assuming that i must have to install billing module + asterisk on the same system as i don’t have enough budget to have a separate system for it.
Your valuable comments are highly appreciated