Why do you think Sanchez would be cheaper? In Salary yes, but not fee wise, not significantly atleast, in fact latest info is that apparently we are enticing Udinese with 35m bid for him (plus would let him play CL qfs for them).
Everyone talks about inserting Giovinco here or there, but pretty sure he would be used in that way at all this summer.
Sanchez makes 700k a season at Udinese and Aguero 5m at Atletico. Both would receive a pay increase upon completion of a 30+ million euro move. 3m a season would represent a fair wage for Sanchez considering what he is currently on, whereas Aguero could ask for w/e he wants considering his reputation and the fact he is a more established player after competing in UEFA competitions for a few seasons.
Media reports are saying Aguero would want 7m season. That represents a difference of 4m a season between the 2. After taxes, and across a 5 year contract, that is a 40m euro difference between players. A massive difference that is hard to justify considering Juventus' total revenue and the coming of FFP.
I agree with your point about people randomly inserting Seba into every transfer, but I feel this is a case where it is actually a realistic and beneficial deal for all parties involved.
For Udinese, they receive a player who would have no problem fitting into their team and whose wages they could afford.
For Juventus, they get a tiny albeit worthwhile discount on a player they want, all the while making their bid more appealing over rivals offering money only.
For Giovinco, he gets to play European football during a season where he is trying to earn a Euro 2012 spot, which if he succeeds, increases his value, something a selling club like Udinese would certainly have the foresight to consider when evaluating our bid against higher cash only offers.
Aguero is certainly the more proven player atm, but any1 who has watched Sanchez grow over the past 2 seasons will certainly tell you the difference is negligible, especially when a 40m euro difference separates the 2 over the length of their contracts.