Add a max cost parameter

We could have a parameter like `--XMaxEstimatedCostAllowed` which would proceed if costs were estimated below that dollar value and halt otherwise.

Start by locating the command-line handling for existing --X parameters and the path that estimates DynamoDB costs. Determine how the dollar threshold should interact with the current operation flow, then add coverage for estimates below, equal to, and above the limit; done means the operation proceeds below the limit and halts otherwise.

Written by the indexing model from the issue text.