[Flashbots] How should MEV Searchers find the correct amount to pay block proposers?

When submitting an MEV bundle (e.g. for arbitrage) a Searcher will pick an amount to pay the block proposer instead of a gas price. This is usually a portion if the profits, such as 80%+.

Searchers might pass it in as an argument to their proxy contract, then transfer directly to the miner such as with simple-arbitrage.

As I understand it, this ends up being a First-Price Sealed Bid Auction. I'm trying to grasp how Searchers deal with this kind of problem. Like what kind of best practices would exist to ensure you're not sending a non-competitive amount OR overpaying significantly.

You can't simulate this sort of thing since it is dependant on the other actors (MEV searchers also bidding), right? Do you just keep retrying the bundle submission, live?

Or do you just have to look the the last block, determine what the "going rate" seems to be, and make an educated guess at what portion of your profits to pay the block proposer?