I am gonna go against all the other advices, and tell you from calcualtion:

1 token at L1 = 150k ...

You need to find free transfers of 14,high quality. 3 stared players at l1 can not be sold, but 4 starred ones can... principels for free transfers:

1) have 14 quality
2) noone else have bid few seconds before deadline
3) have 150-200k marked value (higher value and you can not sell after popping to 4 stars)
4) if you find one with very high markedvalue go for him ofc even if you can not sell... just no bidding war.
5) no bidding wars
6) only use one token pr player you get...

Right this is step one, turning tokens in to cash, you get a more steady steam of tokens (1.25 pr day) than you do of cash, so how to spend your money???

Do not listen to experienced players who have played for a long time and tried to fail promotion just once

The players you wanna go after are 19-20 year olds with the following levels of quality:

L1) 19q and markedvalue of 1M (add 1.3 q and 100k markedvalue on your targets pr week in to age)
L2) 24q and marked value of 1.8M (add 1.3 q and 200k markedvalue on your targets pr week in to age)

When signing long term prospects the principels are simpel:
1) as high markedvalue as possible. You can directly read the tempo they improve from marked value.
2) buy as early in the season as possible... late season save money (and tokens) for next level
3) no bidding wars
4) only buy players listed at lowest possible price... eg you pay 700k for a player at markedvalue of 1.1M and no more.

Why buy players with high price and medium quality rather than low price and high quality?

Because they improve... A player at top talent improve 4-6 in quality pr. season untill he is 23-24 years old... That meens that once you got the player he will during the season become good enough for the next level, and the next after that... Watch training, ALL long term players in your squad should improve at dobble the average pace of improvement... Once they drop below 16 % of a skillpoint pr stretch it is time to get rid and replace...

So you buy players for 2 purpose:

1) to transfer tokens to game money
2) to spend money on players that improve and can play in your team for many seasons (and keep promoting)

YOU NEVER EVER EVER buy a a player with high quality and low markedvalue... It is a complete waste of money. He will not improve (even if he is young), you will get in to bidding wars, he will drop in marked value, whereas the players you keep long term not only takes your team up more levels, but also improve markedvalue season on season...

object is simple... spend the money you have on long term prospects, earn money when you don't have using free transfers close to another star. You will slowly and surely get more and more long term players, and once you feel you have enough, you can start going for even more expensive ones who start out a season young and with 5.9 starred quality