First thing: If you walked in to a bike shop and told them you had a $750 budget (or something similar) and they showed you $1300 bikes, then don't go back there and send the manager a note telling why you won't be going back. That is inappropriate behavior.

Second: Not coasting is fine, but for a 12 RT mile commute on gravel and pavement, sometimes carrying things and sometimes recreating, you'll probably want gears and the ability _not_ to pedal, even if briefly, at times.

Lastly: Bikesdirect and other online places are spiffy, and it sounds like you are a DIY kinda rider, but make sure you have a plan for maintenance and repair before you order online (or C-list or etc.) This plan should include acquiring tools and making available time, if you are doing it, or an established relationship with a LBS, and preferably both so you have a place to go for advice when you get over your head. A local Co-op could also meet this need. A 12 mile RT commute will mean you replace chains every few months, and repack/replace bearings possibly more than once a year.

Otherwise, there are a wide variety of bikes suitable to your need. I commuted on a converted 80's MTB in SS flavor with skinny tires (and later, drops) on a 4.5 mile one-way and 12 mile one-way. I went through a lot of chains and tires, and learned to replace the cartridge bearings on its rear hub and BB. A cross or touring bike would probably meet your needs very well, as could various other incarnations.