I'm posting from my phone, so I'll be a bit brief here, but I'll try to post again when I'm at my computer. I was an econ major, and I completed a masters degree in city planning then worked in transportation planning and affordable housing.
First of all, don't assume that you wouldn't be able to get into a master's program. If you can articulate why you want to be a planner and you get a decent GRE score, a low GPA from years ago can be overlooked. I had a 3.1 undergrad GPA, and I went to one of the best planning programs in the country.
Planning programs seem to like econ majors. It can be tough to attract quantitative types to planning, so a major that indicates some mathematical ability can be a big plus (civil engineering, econ, and real estate development/MBA programs grab up a lot of the more mathematically inclined people with planning related interests, so planning programs make an effort to grab up quantitative types when they can).
Do you have time to do some volunteer work? That's probably a good place to start whether you're going to do a master's or not. I can give some more specific ideas when I post again.