Budget is Key! You can build for as little as 30k or as much as 150k. Top of the line would be Kirkham, Shelby, ERA. Although, you won't build any of these for 30k. If you are in a hurry to drive this Summer. Look @
private for sale here. There are many good cars including FFR, Superformance, Backdraft, Unique & others . You can get good pre-built roadsters here @ good(under 40k) prices. Just make sure to understand what you are buying.
Know the Ride before you Buy! 
While FFR doesn't sell a FIA version, you can get a FIA body via Mr. Bruce & drop on there frame. They are probably the best overall budget (#1 selling roadster kit) build & have a great factory/owners support group.
Welcome to the Addiction! There is no Cure!