Finally a topic that I can contribute to!!!!
I've had several "7 replica's" over the years. 3 were RM's manufactured in South Africa under license from Westfield or so the story goes. They were body & chassis kits that required you to build the rest, but compared to having to build your own chassis and body, it was a long way ahead right from the start. I built my first one in 1994/1995 and used it as a daily driver/track rat/Hillclimb toy. A true do-it-all toy at the time. Fast forward and I still have 2 of those "kits", one sitting on a shelf and the other being built currently as time allows.
I also have a Rotus which was built by Chris Custer in Maryland. Mine has a turbocharged/intercooled 13-B rotary and will be my summer commuter.
Over the years I've worked on quite a few different models, from an original Series 1 Lotus with a replacement Arch chassis, a Maxton Rollerskate, a Westfield MegaBusa, several LoCosts and 2 Rotus'. With ANY of the cars, it comes down to who built it, what their experience and skill level was/is and how much routine maintenance is being done. These cars, in my experience and for whatever reason, tend to rattle every damn fastener loose! Don't know why, but hitting everything with a wrench, loctite and safety wire is a good idea occasionally.
Caterhams are the pinnacle of 7-esque ownership but come with a hefty cost depending on the specs. The most powerful offering is the 620R and is $100K! The most basic spec cars trade on the used market for mid 20's. Westfields, Birkins and Stalkers also trade in the $20's and go up from there depending on engine choice and HP. LoCosts are all over the place, but decent finished examples go for mid teen's.
The 7’s site has lots of great information but is mainly a Caterham discussion group.
The LoCost USA site is where those of us who build our own cars hang out. LOTS of unbelievably talented fabricators post there.
RM-8 in-progress with a Honda F20C engine/transmission and first gen RX-7 GSL-SE rear-end.
The RM body/chassis "kit" just waiting for me to win the lottery.
The Rotus that will be finished up soon.
My original build from 25 years ago.