With 90+ eSIM brands and over 140,000 data plans, eSIMDB is the world's largest travel eSIM comparison site.
bargain for travel: https://gigago.com/esim/europe-uk/
See also: https://www.simonlyfinder.co.uk/esim-only-deals
Boost data only
Unreal roam in Canada and Mexico only
H2O pay for usage
Ultra is only $.02/MB for data; voice/text cost less with H2O
US Mobile "Global Pass", data only; do unlimited US plans do voice/text when abroad?
https://thesavvybackpacker.com/best-uk-esim/
a few under $30 from SIMoptions
data-only: https://cybernews.com/best-esim-providers/best-esim-for-europe/
Three UK: PAYG + data pack £10, eSIM requires contacting a human
https://www.three.co.uk/support/sim-support/esim
Lyca Mobile: £10/20GB, unlimited UK voice/text!
https://www.lycamobile.co.uk/en/bundles/sim-only-deals/#best-value
Physical SIM only:
Orange: €20/12GB, 30min/200SMS
https://travel.orange.com/en/buy-a-sim/offers/united-kingdom
Vodafone: €23/10GB
https://travel.vodafone.com
Also, Talkmobile is very competitive, on the Vodafone network. They allow tethering (hotspot). Uses a physical SIM, not sure if they ship to the US.
Great value for data while traveling. Requires eSIM compatible device.
Also inexpensive domestic service, with hotspot:
https://www.boostmobile.com/shop/buy/plans/
5GB/month only $15