There were three options on my flight:
20MB, speed limited to 24kbps £2.99
150MB, speed limited to 350kbps £12.99
500MB, didn't note the speed limit £29.99

Last time I used the service (in 2017) it was provided by T-Mobile, now the provider is Panasonic Avionics, so it looks like the plans and speed limits have changed. Slightly amused by the cheapest option being half the speed of dial-up internet. Presumably just intended for those wishing to send an email or two, I'd question whether modern messaging apps would timeout with that sort of speed.

With regards to Boingo, you have to pay a supplement (in addition to the subscription) to get in-flight wifi (on any airline with roaming agreements with Boingo).