Your budget puts you outside the realms of the full kit.
You could consider the likes of a Robin Hood with a Sierra as a donor.
When I was loooking into this, the best 7 chassis I found was the Robin hood....or for a bigger engine the Dax Rush. Sadly Westfiled and Caterham had not developed thier setups nearly as well and were falling behind fast (and appear to still be in this state!).
Have often wondered how possible a Robin Hood using a 3.0 Manual Omega as a donor would work out (plus some Sierra parts)
I have been looking around for a Kit Car for over a year, I wanted to build it, so a lapsed build project was the most cost effective way into the scene for me.
My Robin Hood rolling chassis & donor arrive bright and early tomorrow. First builder used a 1.6 Sierra and put all the running gear on. The second owner, only sourced a second donor with a 2.0 DOHC and then stopped the project and finally sold it to ME

It will be stripped right down and started from scratch. I have stripped 1 donor and de-rusted & painted all the running gear from a 1.8CVH Sierra, so I have 3 sets of running gear

I gave the CVH engine away

(now I have to put somthing else in and thought really hard about an Omega engine (I know a bit about them now

)
The whole project is a few months early as I am away all over Christmas & New Year, but the "buy it now" price was a steal.