It's true that the inclusion of teams from the Premier League should also be taken into account, it would be very interesting if a competition for top scorers was created between Mbappe and Halaand. Regarding the budget amount, EPL clubs such as Chelsea, Man United and Arsenal seem to be able to finance Mbappe transfer, even Newcastle will be one of them. However Madrid, which has been eyeing Mbappe signature for the last few seasons, seems to be in first place to get the French striker services.
Mbappe and Haaland, in last three to four seasons, were considered as best candidates to take over dual classic race between Messi and Ronaldo. They actually are young and have long careers ahead as well as top-notch talent to beat other star players. Haaland already moved to a big club, Manchester City, and succeeded in his first season there. Mbappe are aiming to do the same by wanting to move to Real Madrid but he failed to complete it in this summer. I believe soon he will be in Madrid and since that season, Mbappe and Haaland will actually kick off their dual race many years.
Regarding PSG performance if Mbappe leaves, I think Luis Enrique squad will experience a drastic decline, the start of the season without Mbappe has really made the situation clear. Some of Enrique new recruits have also not performed optimally, perhaps requiring more time for the adaptation process in Ligue 1.
Football is not like math and now with great contributions from Mbappe, PSG still have bad results. If football is like math, PSG will play worse without Mbappe. But if Mbappe is no longer there, PSG will have other players to take over his position and key role. They even can buy new star players to rebuild their squad or they will not spend huge money for it, we don't know about PSG transfer strategy for future, now.