The thing is that you don't need to spend £500 to discover that there is a lot more traffic up there than you thought here was. I can tell you that for free
Except outside the UK, when there really isn't much...
You can also discover it for free by flying under a radar information service, with three passengers who do nothing but look for the traffic reported to you, as a fun exercise. If you can spot 50% of the reports you are doing very well.
Then there is the other god knows what percent who fly without a transponder. These are evident from reports like "traffic on a reciprocal heading, distance 1 mile, level unknown". You are obviously looking like hell but can't see anything. You switch on all your lights just in case. You are at 4000ft, he's at 800ft but he doesn't have a transponder
Statistically, the case for spending money on collission avoidance is very thin. Just as well, given how many people don't really want to be seen.