You're doing deliveries - the bike is going to get knocked around and, maybe, stolen.
Buy a second hand bike. Just make sure the bearings are greased and adjusted (which is why loose balls are good), the chain is oiled and the wheels are true - all stuff you can do yourself. Keep your better bikes for when you're NOT doing deliveries.
I'm with Scrod on this thread.
I had a good bike ... so I FIXED it