Well that certainly puts a different spin on things!
The problem is going to be the fact that, even in metal, 20mm figures are generally slim in comparison with most 28mm. Each scale has its own conventions.
Given your requirements, may I suggest the Foundry Pygmies? They make three sets. Here’s one:
Most of them are archers,but it would be a place to start.
Not US,of course,so there’s shipping to take into consideration, but I believe VAT is removed for overseas sales.
And,until January 5, there are multi-pack deals to be had,the best of which is buy 16,get another 6 free. That would bring the average price per fig down considerably, probably within range of what you’d pay for 20mm.