I get that, but I don't think it's the difference you think it's. It's different, but there's not difference (if that makes sense). If a guy is on the trading block, you're competing in the market for him as well. Do we really think that the Red Sox were the only team in the market for Chris Sale when they traded for him?
Yes, you have to pay the guy money, but you gotta pay someone that money. If you want to trade for a true ACE, you can say goodbye to guys like Mayer/Bleis/Anthony (although I'm sure a team would want some pitching prospects as well. So a package more like (Bello/Mayer/Anthony) likely gets you the deal.
Yes, now you don't have to pay that guy, except in 2-3 years you probably do anyways, and now you have to pay to replace Bello, you will have to spend money on a SS now, and probably an outfielder too.
Next years free agent class is good for starting pitchers. In my opinion, it would be very unwise to sit on the sidelines. You have also just reset, and have a boatload of money coming off the books sitting well below the cap. Houck/Bello/Whitlock would look pretty amazing with a true ace leading them AND knowing we will have Mayer behind them in a year.
You can't buy a winning team with money alone, the Mets are proving that this year, but that doesn't mean you shouldn't strike when the iron is hot either. Next year is shaping up to be the right time to go big for starting pitching for this Sox team. It makes all the sense in the world.