In Sweden we have group E and F, cars older than 12 years, floating age.
Gr E: >15kg/kW, typical car Astra 1,6, Golf GT 1,8 (1986) Golf III
Gr F: >12kg/kW Volvo 940, Golf GTI, etz.
Strict rules. No changes in engine and gearbox. All safety devices needed like rollcage, seats, belts etz..
Used cars for sale from 2500 Euros (25000 SEK) in Sweden. Almost as fun to drive in rallies... :)