therd is several options out there. the jessops portaflash works but the quality is a bit on the questionable side, then have the interfit ex150-200 kits and the lencarta. these sound better than the portaflash. you then have the bowens/elinchrom d lite 2 head kits, which are the better end of the budget range. for buildability you could buy a single professional head with as much power as possible from the bigger makes and use that with a reflector till you can afford a 2nd head.
personally i chose the elinchrom d lite 4 2 head kit.