Hi Steve,
Not sure if you are the same Steve I have replied to via private e-mail address?
Anyway, the answer to your questions:
Yes, in Tabac shops you can buy the 214 envelope for 50c
You are actually paying for the postage, not the envelope.
These are also available in your local tax office alongside the 214 form, as some people don't have internet and hence cannot complete the 214 form online.
I have to admit I recently had trouble getting an envelope from my local Tabac, they had applied for them but the tax office said "No"
Maybe, they are only supplying them via tax offices from now on?
Take your completed 214 form to your bank, the online version, all 3 parts, will be accepted.
Whether they can supply you with an envelope is a poser!
My bank initally said no, then on being pressed, found some in the stock room and said "hope this will do".
This has happened to me for the last 3 years!
You will be give part 3 of the form back to keep.
This is your proof of payment, hold it with your Escritura as if ever you sell, you will need proof of ALL payments on your property.
Good luck with it and please let me know how you get on.
Kind regards,