I think he means that it's expensive, no matter what. It's not cheap to do if you have the market lead. It's always expensive to buy them.
Btw, here's the real interview. http://www.gamespot.com/articles/xbox-one-interview-phil-spencer-on-microsofts-firs/1100-6429471/
Put it this way, whatever Microsoft paid to get Tomb Raider as an exclusive for about one year, Sony wouldn't pay half as much to get the same deal because they have twice as many consoles. They'd still be paying a large price. I believe that's what he meant.
Makes you wonder if the year head-start MS had also gave them a big advantage on the exclusives/timed deals they got last gen - maybe also explains why both didn't want the other to have a head-start this gen...now the 'dust has settled' Sony are in a much stronger position (compared to last gen) due to h/w sales and as such have managed to seal so many deals (CoD was a massive win and statement of intention IMHO).