Unless I glossed over it, no one has mentioned planning out what you want to buy and buying it a piece at a time.

Say you want a Kadet Senior kit, a .56 size engine, 6 channel radio, plus the finishing items (tank, glue, etc.) If you can't afford to drop $390+ for a RTF kit or like me and WANT to build your first plane, why not just by the kit and what building items you can afford and build it to the point you can go no further without more components. This also assumes you can leave a half assembled plane safely out for a period of time.

If it's your first plane you likely aren't gonna build at a record pace so it should give you time to save. They aren't going to stop making the engine and radio to like anytime soon. If you're lucky you might stumble upon a deal in the mean time.

The only thing extra this costs is patience. So if it does cost $500+ at least it is over time.