When I started looking for GT40s in 1999/2000 I found the same thing that Howard did. GTD was just going out of business at that time so that was not an option. Tornado was available but I couldn't find anyone in the US with one, and their agent in the NE was incredibly unhelpful (This has changed, call Andy direct and he can help you out).
ERA's were available as well but were simply out of my price range. At $54k with a lot of sourcing to go in order for the package to become a complete kit, I couldn't afford it. I learned more about the NZ and Australian outfits that Howard mentioned and spent a lot of time with NZ GT40 and RF in Australia, with the rest of what I did probably being well known to most on the forum as I bought an RF kit and am now waiting on a turnkey.
But, more to the point, I think find ERA's GT40 market position unenviable at the moment. I do think they produce high quality cars and one of the best on the market for sure, no question of that at all. But I don't feel that they are untouchable for quality, performance, etc. these days because things have changed a good bit since they started offering their replica.
The new CAV cars are gorgeous and seem to be excellently done with the new improvements on current chassis cars. The Superformance car seems to be more accurate (metal roof, repro transaxle for BB, lots of in house exact fab parts) than the ERA for those looking for that sort of thing, and it is a turnkey minus for around $75k (with CAV being about the same price, come now, you're going to get some options).
And then RCR's offerings look very tasty indeed for more in the way of monocoque cars that you can build, as well as RF and GT40 Australia with tube frame cars in the US. RF is tooling to go turn key minus like Superformance and CAV are now, so all three will compete in the turnkey market for US business and will probably do so fiercely.
I think that ERA is producing the same high quality car they have always done, but, they have not altered anything to combat the new offerings on the market. This doesn't mean that ERA isn't as good as the other cars, quite the contrary, they are still an incredible car. I think that the other companies have come to, and in some cases surpassed, ERA's standard they set so many years ago and are simply doing it for less money. ERA set the bar and it is a fantastic standard, but the market has changed a lot in the last ten years. Obviously, some will take issue with what I've written but I am simply writing it as I see it.
No matter what you choose you can't go wrong with the current crop of GT40 replicas. Seriously, it is a lot different than it was 6 years ago when there was not much to choose from and some weren't even replicas much at all (T3, Lone Star).
Ron