The thing with Baines is that he is definitely irreplaceable for us in his position. In other words, even if we did get 20 million and were prepared to splash all 20m and his wages on another left back, there isn't another left back in the world of the same quality that we could get (the ones who are as good are all at CL/championship contender clubs).
Having said that, left back does not have to be a priority area for the team. If we sign a solid left back for 5-6m and use the rest to buy a top notch midfielder/winger, the team overall could actually gain more than it loses with Baines' departure.
In addition, every time I've seen Oviedo play I have been impressed. Perhaps he could do a job for us there... he's definitely a great back-up in that role anyhow.