Using camera flashlight of the camera using remote?

I have Nikon D5100 and it lacks wireless flash capability. But i want to use flashlights off the camera. I have googled for various options including cactus and yongnuo products for wireless remotes for controlling flashes but didn't understand which one is better. I think SU-800 will do the trick but since it is expensive i need some inexpensive alternative mentioned above(cactus, yongnuo etc) . Also recommend flash and remote best suited. My budget is 400$( may be bit more) .

I recommend the Yongnuo YN560 fully manual flash, plus RF602 triggers. The flash costs around £50, a set of triggers around £20.

These will give you full manual control, but no TTL (auto flash metering). Tbh it's better to learn how to light manually in any case.

I use the Yongnuo flash along with Nikon speedlights (also in manual mode) off camera with my D300. The flash has always been reliable & the triggers have great range.

Here's a Strobist swim shoot I did with 2x YN560's and a set of RF602's;

but a lot of my photostream uses off camera flash too - a recent example;

With the money you save on buying expensive (& unnecessary) Nikon products, you can also get a lightstand & modifiers (umbrella or softbox) - essential if you intend to shoot fashion/portraits.