Neewer VK750 II I-TTL flashes are 55 bucks on amazon. I bought a second one I like mine so much, works great on and off camera and does exactly what I need it to do.
You can use your on camera flash turned down to low power to trigger the speedlights, when you camera flashs goes off it fires the speedlights as long as you have the speedlight and your on camera flash in the right mode it works great.
If your looking to get inexpensive flashes I think these are the way to go, I have never used a high end speedlight before so I am not really sure how much more you can do with those but I these work for me. I don't need anything better and its very easy to use.