Definitely get yourself a teacher before the bad habits creep in - if they already haven't crept in!
The violin is not an easy instrument to play and bad posture and technique will hamper your playing, even with simple tunes and pieces.
If you've watched good violinists play and you think it looks easy, then remember that they will have spent many years being guided by teachers and spent countless hours practising to develop the technique that enables their playing to look effortless.
As Rhapsodin said, even one lesson every other week would be better than none at all. One-to-one tuition for the violin is essential if you want to make progress and I'm sure there are teachers out there who would offer a half hour lesson, especially if you explain how much you want to learn but cost/lack of cash is an issue. In fact, to begin with, half an hour of one-to-one tuition is probably going to provide plenty for your brain to assimilate.
Amanda