The Vulsini kit is very expensive so probably not appropriate. Also it doesn't heat evenly as it only heats from one side. I checked it and found quite a lot of variation between the stones that are next to the heating plate and those that are away from it. Stones in the corners are also cooler.
I would disagree that there isn't much variation in price. I've seen very reasonably priced kits and very expensive ones. eBay is very good for shaped stones.
Another thing to be wary of is that quite a lot of stones have chemical wax or epoxy resin coatings. There are probably 2 reasons for this:
1. It turns them black. Basalt that is suitable for hot stone massage tends to be dark grey but turns black when oiled (seasoned) or wet. People see used hot stones that have been oiled (which are black because of the oil) and think they should be black when you buy them. This is completely wrong. Although naturally black basalt does exist it tends to be more coarsely grained making it unsuitable for hot stone massage (there are a few exceptions, but these are extremely rare, and where I have seen them they have all been natural pebbles, never shaped stones). If you've ever been to Bali, where there is a lot of black basalt used as blocks in construction, you will know just how coarse it is.
2. It fills in holes. You may think that this wouldn't be such a bad thing (apart from the chemicals coming into contact with peoples skin - more of an issue with the wax than the epoxy resin which sets hard), but it makes the stones too slippery for use as working stones and may cause placement stones to slip off. Working stones need the texture of a natural surface to provide that little bit of grip with the connective tissue when used for effleurage.
Some sellers do photograph oiled stones, but if they don't tell you that that is what they have done then the likelihood is that they have been treated and are best avoided.