I'm admittedly a bit biased against and not very experienced with flash photography, but I'd recommend your next photography investment be a good prime lens (like the Canon EF 50mm f/1.8, which is only a little over a hundred dollars).
The kit lens and presumably your telephoto probably struggle in low(er) light conditions, and I can understand why you'd want to explore flash options. But a good prime will allow you to do a lot more with available light, produce beautiful image quality (and bokeh!), and force you to engage more with your subjects and think more about your photographs.
I don't know if you're already well versed in the foundations of aperture, shutter speed, ISO... if you aren't, I second Miking's suggestion of cycling through everything to understand their effects. Try shooting in full manual mode making use of all the settings, and you may find that even with the kit lens you may not need the flash as often as you thought.