To the OP- if getting started in the hobby on a tight budget is your goal, you have to think about all of the costs, not just fuel. Yes, it's true that gas is cheaper than glow fuel. However, that may not make it the cheapest option.

You could start with a .40 size trainer and use a 10cc gas engine on it. That engine will cost about $50 more than an equivalent glow engine. It will probably take about a year to recoup the cost in fuel savings.

Also consider club fees and such.

If cost really is the biggest issue, consider some of the smaller electric planes. You can get going with one of those for about 1/2 the cost of a glow powered trainer. Being smaller and lighter, they don't handle the wind as well. But sometimes that's what your budget can handle.