So far, the Wisconsin recount is costing a lot to change little -
https://www.npr.org/2020/11/28/939645865/biden-gains-votes-in-recount-of-milwaukee-county-requested-by-trump
I really hope ordinary people aren't donating their money to a lost cause. Those numbers don't look like a good use of $3M to me.
Recounts
rarely make big changes to the counts. That's why there is frequently more than one recount until a decision is made. An alteration of 136 votes out of 460,000 is a very small change.
If after several recounts a result isn't achieved, in the UK the returning officer settles the election with a coin toss. This doesn't happen very often
We do our postal votes differently to America; the ballot card is the same as the one used in polling stations, and are added to the bags of cards from them. So the counters can't tell what are postal, or physical votes.