Here in Ireland the 80i's are ~€144, and 225i is ~€339. No way are they worth twice the price of the 80i, in my opinion the difference is small enough you will need a good quite source to really appreciate the difference, plugged into a regular computer or generic sound card i would struggle to appreciate the difference. You would be better off buying the 80i and spend the extra €200 on a good dac/amp combo instead.
To really throw a spanner in the works, i wouldn't buy the 80i at all, the Alessandro MS1 is a far nicer headphone and will probably work out cheaper too. I own the 80i, MS1, and 225i so you could say i'm very familar with the difference between them, in fact i listened to them all last night back to back while testing a cheap DIY amp so the difference is fresh in my mind.
The other side is you might not like the 80i or Grados at all, better to find out with the cheaper pair. If you do like them, well i'm sorry for your wallet as there is always a higher model to aspire to, and before you know it you will own four of them