@edolnx It's been a while since I did any BGP stuff, but from a few quick searches, I believe you can advertise your ip blocks, even the IPXO leased ones, through any RIR.
You just need an org ID. Which seems to me that you should be able to establish an ORG ID with RIPE and still advertise BGP through US providers.
@edolnx ARIN posts the fee schedules, you could always set up an org id and ASN there, and advertise whereever.
They say its $250 a year which is down from the last time I checked.
@edolnx Have you reviewed https://www.arin.net/resources/guide/request/ ?
You cannot obtain an ASN in the ARIN region as an individual. So that means some sort of state issued business registration.
Look at the fee schedule page for costs, you can probably expect a few hundred USD per year.
ARIN support is good to work with, but there may be more "process" and paperwork than other RIRs. Create an account and open a ticket to get the process started.
Note, you might want to just use RIPE. It might be easier.