How to jailbreak my iphone 4?

Its locked to verizon service wich is too expensive for me

Thth

Jailbreaking really won't help you with this.
You have a CDMA iPhone 4, which can't really be unlocked. You're pretty much stuck with Verizon.

There are some services out there that will flash your phone to other carriers, but they usually will charge you about $100.

Consider looking at PagePlus. They're a virtual network. Basically, they "piggyback" Verizon's cell towers, but charge much less. You'll still get the same coverage that Verizon offers, since you're still technically on Verizon's network.

Just look up Verizon MVNO in Google and look for virtual carriers that interest you.