No you can't. That's why the buying coins thing is so big, it's not because they do them at some cheaper rate than EA, it's because EA doesn't do them period. You can only buy packs from EA and buying packs for the purpose of turning them into coins from on-selling what you get from the packs would not prove very worthwhile unless you got very lucky.
Let's say you want Ronaldo, well you're going to need to get very, very, very lucky to get him out of a pack (you could spend hundreds and hundreds and hundreds of dollars on packs and still not get him), or you could win games, do some trading, work the market to save up a million coins which obviously takes a lot of work.
Or, you could just buy a million coins from a third party and buy Ronaldo straight away. Buying coins creates a pay to win environment, though most of the players I encounter with hugely stacked teams are bad. A million dollar player can't make up for having two dollar skill.
When you're simply able to buy points, there's still something of a pay to win element, but buying packs is rarely worthwhile, it doesn't offer that big of an advantage.