Take care, if you get promoted there will be better players on the market (quality for level 2: 3* 15-19, 4* 20-25, 5* 26-29).
So making now an expensive transfer might not be the best strategy. It is also true that the first days of the new season will be madness,
since people got fresh money and saved tokens.

But you can prepare for it. Manage to get a good starting 11 and get rid of players now you won't need next season. Since next season they will be one years older and their market value decreases. That way you won't be in a hurry to do an expensive signing, but you can wait until the transfer market calmed down.