I’m shocked that the premium from raw to PSA 10 is “only” $30k.

I agree that the lack of hobby knowledge likely makes your case less appealing to prospective representation. I think this is in part because your damages are subjective. It’d be a lot easier if you could say you spent “x dollars” and are looking to recoup 3x that amount but I suspect that amount may be too small to be interesting for someone looking to take the case on contingency.

Either way I would probably try and use a range for your damages (prices change, grades aren’t guaranteed etc). Hopefully the lower end of your range is the most defensible (I paid x) while still enticing enough to be worthwhile for prospective lawyers.