Frogbits grew faster than I expected, so holding them in a holding chamber at the moment.

Frogbits: 10 floating units for $5.
Water lettuce: 5 floating units for $5 (with full roots intact!). These are the same water lettuce ebay/aquabid is selling as 'dwarf' water lettuce.

Frogbits are free of duckweed and snails.
Water lettuce comes from my main tank, which has snails (but no duckweed).