Rangers are in a shitload of debt so it's fair that only 60% of transfers get put back in the transfer budget.
First option; Marco Verratti. If you get him at the start of the game, he can cost you around £500,000.
Another good player is Vincent Enyeama. Starts off at Hapoel Tel-Aviv. I've not had much experience with him, but according to others, he's a great goalkeeper.
Strikers isn't easy because you'll have to put in a decent amount of money to get good players. If you want to strengthen this part for a season, I suggest Erjon Bogdani from Chievo. Rather cheap, but a good targetman if you feed him the ball in the air.
I've left defence until last and that is because the defence is like the attack, not easy, I've found, to find cheap defenders. If you've still got the money, then go straight for Otamendi, plays for Velez. If you don't, then look around the free transfers for experience, I think Jorge Andrade is still in there.