I'm unaware of current costs of chinchompas as I do not play anymore, however, when I went from 80 - 92 range I used chins. The effectivity on chins is purely based on what gear you will be using when chinning. The gear alone can save you millions. Therefore there are variables which have to be taken into consideration to estimate how many chins you will need. 50k chins is a good start, however I think it can be lowered down to almost 36k chins, I don't know which are better red/black but I researched on a forum and found this,
"Black chins are better but unfortunately I wasn't able to find out how much better they were.
I'm getting 570-600k Ranged XP from 2500 Red Chins at 91 Ranged using medium fuse. I don't know if that's bad or good. "
I think I used medium fuse, reds, and around 20k chins for 84-92 range.
4k per trip, was very quick.
To end, use the best gear possible, the fastest way will always be the most expensive, the shorter way is always substantially cheaper.
Goodluck!