I think the main difference in price is whether you try to get one from a store in North America (such as Kellam) or directly from a store in Finland. Lamnia in Finland seems to have the most decent prices, along with Varusteleka (if they are ever back in stock there). The latter are known to be fast and cheap where shipping is concerned - one rate no matter the size and weight, so add some other fun stuff, like socks or chocolate.
There are indeed other makers of 'sissipuukko' knives, particularly Marttiini. If my info is correct the word stands for 'guerilla knife' or 'ranger knife'. All referring to Finnish soldiers trained to fight as guerilla infantry in the arctic forests. Varusteleka does not call the Terava knives 'sissipuukkos' but 'Jääkkäripuukkos' or 'Jeager knives'.
The newer Peltonen knives are indeed not quite the same as the old ones. Better steel (80CrV2), possibly a better blade maker (Lauri, known for very good puukko blades), thinner spine (4 mm instead of 5), high flat grind instead of a full flat. The sheaths are still the same with the patented rubber wheel retention system. The basic blade stock from which Lauri makes the blades seems to be the same as that of the Varusteleka Terava knives. The shape and grind are very different however. Take the whole of both ranges and you have 4 sizes of more or less similar black rubber-handled, militaryis puukkos to choose from, take your pick.
I think you can't go wrong with either the Peltonen or the Terava (disclosure: I have both so I can compare), but getting them from Finland direct may be a lot cheaper (I don't know what happens with import duties etc. into the US, a North American shop will already have taken care of that but the markup seems to be substantial).
Note that the M95 can be had with either a leather or hard plastic sheath, the latter also being usable for lefties. The M07 is only made with a leather one, although Lamnia has a 3rd-party Kydex version for it as well (but as you can't order the knives without any sheath, you'd have to buy the M07 with the leather sheath and then add the Kydex).
Hope this helps, even if a bit late. ;-)