KVA used to be a fourth company in the UK, in fact Ken Atwell got the whole GT40 replica market off the ground with KVA, but he sold it to a US firm, Integrity Coach Werks,Inc. The GT40 replica club is VERY useful for sourcing parts and for finding people who have done before what you are trying to do. The address is on my GT40 page. The club can be helpful wherever you are in the world, we have members in the US, Australia, all over. You can make the total price less by buying some parts yourself - the GT40 Club is a good place to do this or to find out what it is you are looking for.
Some parts can be second hand or reconditioned which saves even more.
In addition to these UK manufacturers there are several other companies around the world producing GT40 Replicas. Check out the GT40 Website Index page for full details on all the ones that I have managed to find so far. You need to spend a considerable time talking to each manufacturer about their specific programs before making up your mind. If you decide to buy a UK kit, I would strongly suggest that it would be a wise investment to take a trip across here and to meet with them before deciding. You would also be very welcome to join in one of the Club events.