What is the best kind of accommodation to fit two adults for a month, I'd be willing to pay up to 2,000Z£ just for the accommodation.
For that price you can expect to rent 2 or 3 rooms in quite comfortable flat, well equipped, with internet and tv - near/or in the center of a medium sized city, maybe in not much popular area like at the see or in the mountains, but for example in the town like Malbork. Of course more "holiday" places are also available with this price, but them may be smaller, and not in great location.
Renting in Poland implies that you will pay the fixed rent rate plus electricity and gas mostly.