I have 20 3 watt led each light runs 2.4 vdc @ 700 ma each. I need a constant curant led driver but am not exactly sure what size driver to get. I just want to make sure i dont burn out $100 in leds.

 

get 2 x Meanwell ELN-60-48D constant current drivers.. about $35 USD each. Very easy and dimmable via a 1-10VDC signal.. Run 10 LED's per meanwell in series. You will need to adjust the dimmer circuit voltage to get 700mA as they will go higher (1.3A) and there is an internal pot to be able to dial down the current -25% or so.

If you don't need dimming I'd go with the Meanwell LPC-35-700 ($15 each or so) preset at 700mA.