Optima's go for 10K and up more or less, a 1SM Outlast should go for around 3K more or less.
Good Read about batteries (Deep Cycle and Normal Lead-Acid car batteries
http://www.uuhome.de/william.darden/
http://auto.howstuffworks.com/question219.htm
Basically the biggest difference is that a Deep Cycle Battery is designed to withstand several hundred Discharge/Recharge Cycles that a Normal Lead-Acid can't do.
I wouldn't recommend listening to the radio with your engine off using a normal battery, it would be a hassle not being able to start your car even tho you have jumper cables. Well if your battery is still under warranty you could always call up motolite and have them deliver a warranty replacement or a new battery
