4-channel preamp out put
but no "sub preamp output"

do I want a sub preamp output?

is it worth it to spend an extra 100-150$ to get one with it (the deck I am looking it is used, and if I want to get one similar will have to spend the extra)

 

100% depends on if you plan on running a sub or not. Don't think you'll be running a sub? Then you're set.

 

I will be running a sub,

 

The biggest advantages of a sub out on the deck is usually a built in crossover and level control. If your sub amp has a crossover and a wired level control then you could get by without the sub out.

 

Also, if you transport people that aren't exactly friendly to large bass hits, you have the option of turning the signal to the amp off, thus turning the sub "off" for however long you have those passengers.