For those who care about using the 3 UK sim products, they just had a price reduction at Amazon on a 4Gb data, Unlimited Voice & Text product. It is currently listed at $9.45 with shipping of $5.62.

I ordered two for a total of $12.26 each for a trip in late March. The delivery is from the UK so mine are scheduled to arrive March 3rd-6th, but that's fine for my travel plans. The seller is shown as Three Mobile and there seems to be a limit of 3 per order, possibly based on the shipping fee per order. My order only had the single shipping charge, and with 3 sims in the cart the fees stayed at the $5.62 charge.

This seems to be about as cheap as it gets for data & voice Euro roaming, and the consensus is that this product performs acceptably.

Edited to add a link: