Well, it does depend on how much you want it!
There's not much in the kit - a new resin tank and seat, some metal parts for the exhausts, beautifully machined silencers, decals and an etch fret. I paid £45 for mine. The resin bits are very well done, nice and clean as you would expect from S27. The only suspect bits maybe the white metal parts, but this only means some test fitting and trimming. To get an accurized 79 bike does require some work to the swingarm from what I've seen.
I'm biased of course, but I think it's worth it. Of course you also have to consider, what other choices are there for a 1979 Sheene Suzuki??