It's an incomparable situation. The Portugese league has much looser regulations regarding transfers for non-Euro players. Brazil and Argentina is bursting at the seems with young, cheap, unproven talent, but English leagues are effectively only able to transfer in the proven ones (e.g. players from these countries making a certain percentage of appearances for the national team, or if their transfer cost is over £10 mil I believe?). Porto and Benfica get a lot of their talent on the cheap this way.
Their league also allowing third party ownership of players is another huge difference over the PL. Leads to a lot of teams only needing to pay, say half the amount when bringing in their players.