Try finding out where the corporate operators are in your area and then go knocking on hangar doors handing out your resume, offering to do any kind of work in order to get your foot in the door. Many corporate part 91 operators like to hire low time guys and put them in the right seat, probably because they can hire you for cheap, and because they know you will stick around while. I know of at least 2 friends of mine who were hired into a jet with around 500 hours.
In the meantime keep instructing, If you work hard you should be able to build another 500 hours in about 7 or 8 months and with a 1,000 hours total you should be able to get that $19,000 a year regional job you've been dreaming about!
Personally I would forget about the airlines and persue corporate / charter operators. Better money, better job security.
Also, if you can work your way up to 1,200 hours try applying to the night freight haulers, which is a great way to build your multi engine time and gain great experience to further your career.