Honestly, unless things are remarkably different at this 1500, your best bet is actually to check your local Gander Mountain and see if they have it on sale (literally the only time you'll hear me say that, as their ammo prices are normally absurd). I've picked up a decent amount of American Eagle 5.7x28 for $23 or less a box. At the 1500, they have been much higher.
Now, if you are stuck with your heart set on actual FN 5.7, then you might end up having to pay a premium.
Though PSA appears to be selling FNH 5.7x28mm 40gr V-MAX 50rds SS197SR for $23.99 a box right now (plus shipping).
FNH 5.7x28mm 40gr V-MAX 50rds SS197SR
If you buy one, take it from me. The next gun on your list is going to be the PS90. Who can live without a matched set? The damned things are addictive.