ASP for iPads has been ~$600 in the past. It might drop a bit, now that Apple has lowered the entry price point (or could rise, as LTE pulls more people away from WiFi only).
It costs them around $300 (Can't say exactly, however the LTE version was pegged at $330, could be less depending on volume deals) they are making a sizable portion of that 1.8bil in net profit.
$1.8B in revenue in a weekend, still not bad :P