If you don't have an SO, do you really need the second phone? That's the only reason I've had one, it seems as though you're cost conscious so it's worth asking.
Some gentlemen on here kept everything super secure and see only high end, secure ladies and sort of overdo security. They may have a lot to lose, I don't.
I'm frugal as hell but I don't even worry about not using all the minutes. So you have too many, they'll be there when you renew. I used a net10 phone, and when you get a cheap one be prepared to say 'pardon' a lot because they don't sound as good, and texts require more button pushing. Also, if you go inactive for some time, you'll still have minutes but they might have to send you a new SIM card, so reactivate before a heavy hobby opportunity.
Seriously, ask yourself what you're doing, if you need to go all James Bond counter-espionage. Security is important but all things in moderation. I only got a second phone because my SO gets the phone bill.