When Kraftwerk tour the UK there’s always a right bun-fight for tickets - less so for when they do festivals
The GA price is on tier 2 now. Rebellion was announced last week too, and I expect there’s a fair amount of crossover with ticket holders. With a capacity of 25k I think this will sell out, but it’ll take time
If you enjoy the line up I wouldn't let the festival location put you off, we went into it sort of blind in 2019 and I was really impressed with everything. We spent our first night in Gdansk as it's easier to fly into their, but Gdansk, Sopot and Gdynia (where Open'er is held) is known as the 'Tri-City' Area in Poland and it's really easy to just bounce between them on the train.
20 mins on the train from Gdansk to Gdynia the next day, had an Air BNB and just commuted up to the festival each day via the shuttle bus from the train station in Gdynia. Buses run almost every 2 minutes and it's always so easy to get to and from the festival.
As @gingerevans84 said, plenty of beaches around Gdynia and Sopot to recharge and everyone was really friendly with us when we were there. As an experience I found the whole of our time in and around Open'er an underrated experience on the Euro festival circuit.