Try Razvan Rat. You can get him for 3.7mil (mfr clause), although depending how far in you are then he might be a bit old..
Davide Santon is another good player who can play left back (he's really a right-back but can play both). From Inter at the start (might be on loan at Cesena) but after the first season he's more likely to have been released or sold on. Costs about 5mil unless he's broken into a first team squad. Most expensive I've seen him is about 10mil.
Domenico Criscito is also definately worth a look into. Can also play CB/SW. From Genoa or Zenit (depends on patches).
One of the best Left Backs though is Fabio Coentrau, but he is almost certain to be very, very expensive.
Also there are some other which are good for bolstering you'r squad (injury replacements etc) who you can get on the cheap: John Arne Riise, Balzaretti, Maxwell, ****, even Charlie Mulgrew can be good if he's at the right team with good training.