I chose Spain to save in travel costs (flights, visas etc. involved in going to the states again)
Flight to the states would set you back about 700 EUR.
With Avgas at $5 / gallon instead of $15 / gallon and dry rentals about half the price from in Europe, You would start benefiting from around the 25th hour.
If nobody instructs you (apart from checking out the aircraft), why would you need a VISA ? And if its occasional instruction (the "experience" days that you refer to), a B1/B2 would be sufficient, which is valid for 10 years.
Spring is on the doorstep so the [UK] weather will improve
It depends on the time and flexibility of the OP. My experience in trying to schedule flight training / hour building in the UK is not a good one, mostly because of the sh1te weather. Spain, Greece, Southern France and the US are much more reliable in this sense, especially when stretched out over a two month period average.