There should be a few threads around with advice on who to buy. Good and cheap players are always being shared about by people.
There's no need to rush into buying players but it's important you get who you need rather than wasting money on people you won't use. Buy Babangida from the PES shop for 150 PES points and try to buy him in ML mode. Other positions you need to buy someone for asap are CF, GK, OMF as well as Baba for SMF. With a strong spine to your team, you should do fine.
A good idea is to find players near the end of their contract by doing a Conditional Search for players with 0-1 length of contract. If you try to sign them halfway through the season, if you're successful - you'll get them for the start of the next season. Someone said they got Totti and Henry this way. Not bad, hey
Plus the usual advice of playing players on better form arrows can help quite a bit in ML mode.