The vast majority of turbine jobs are multi-engine, so the ME would be required for a low-timer interested in corporate or airline jobs.
However...there have been large cuts in regional airline flying in the last couple of months, and two airline bankruptcies in the last several days due to high oil prices and the slowing economy.
Low timers (less than 1500-2000 hours) will not be getting hired at airlines for long, almost all majors and most regionals have stopped hiring within the last two weeks. Even if you do get on, you will be one of the last hired and will either be stuck at the bottom for a very long time, or furloughed.
In your case I'd say get the CFI so you can get a job now and make some money. Then get the ME as soon as possible, so you can build ME time whenever you get the opportunity. When hiring slows, you will need 300-500 hours ME time to get a regional job. CFI jobs are more stable than regional jobs...9/11 didn't affect me much as a CFI. Find a good CFI gig, make some friends, and have some fun for a few years.