That's one of the reasons I'm against giving up 2 real early picks for a WR like Ocho. Roy Williams maybe, because he's relatively young.
But 2 late first round draft picks give you a good shot at getting cornerstone players for your franchise for a long time. Even if their contracts expire, you have franchise options, and get some compensation if they leave and were good players.
But, as the original post brings up, the finances are a big part too. To snag a top player from another team, costs a fortune in signing bonus and salary. Signing guys at the bottom of first round is not usually going to cost the same, plus they are younger and should have more tread on the tires. If they get injured for a year, it's not ballgame over hopefully.
AdamJt13 might be able to give us the annual cost of guys from pick 22 and 25 in draft in an annual cost for their first contract versus what Ocho made annually over his current/last contract. Roy Williams and Boldin too.
As you mentioned you probably get 2 or 3 rookies picks at the 20-32 range for what an Ocho cost or would cost you to snag him away.
LarryCanadian