Ask parents or a really good/close friend, or hope they’ll maybe add PayPal in the future
OR just get one of the prepaid CCs, I’ve lived with one of those for a long time as well, they work pretty nicely.
I pretty much missed out on UE3, but if things are even remotely as they were in the UE2 days - and from what I’ve seen so far not much has changed in that matter - the Unreal dev community is one of the best!