Garmin Nav Com £3114 or £3834 inc VAT.
Most light GA with a full C of A will have a Nav Com or two. Most of the club aircraft I see have either old King 170 series or newer KX155/165 or the Narco equivalents. Even if they have a 430, they might have an old 170 series as second Nav Com.
So, for someone with an IMC (or IR(R)), the potential cost of going 8.33 compliant might bebetween £6k and £9K?? plus installation. Total spend might be 50% of the value of the aircraft. Will the aircraft be worth any more?? No but the ones not 8.33 capable in 3 years time will be worthless.