you have to decide if you logistically can live with infrared thus saving TTL , or if not possible (most likely) then you have to go with radio frequency.
if rf is the awnser youlll be doing manual exposure anyways, i hear nikons SB 24's and 28's can be gotten around 60-90 bucks. doesnt make sense to pay 250 more bucks to only add like 25% more power for the best nikon flash.
better to add another flash you can more evenly spread out your light.
Also its about 100$ per flash for good (600ft) recievers, (elinchrome)
200$ if you need to go like 2000 feet.
(pocket wizzards)
dont mess with the 30 buck poppers
also the transmitter is 100$
stands can be 20-50 bucks each, fits for the flash to a normal brella stand are 15-20 bucks.
problem with ir is its spotty, and range isnt great. weird things can make it not connect, its line of sight basically,
cant shoot with 3 lights behind you or at odd angles, which is the boon of fun portraits. screw it, go rf