They aren't too bad in price.
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If you guys truly buy peisteskin maps and don't get bluebird that means:
1) you got gil
2) it cost less to buy bluebird
Also the reasoning of "why put something hard to get into casual content" is useless - not having bluebird doesn't affect in any way your chances to progress further on endgame content. Bluebird is just a nice item you can accidentally get and then decide whenever you want to get some gil or use the minion for bragging.
I got one doing peisteskin maps with my FC a couple of months ago. The way we handle our drops is that whomever opens the map gets all of the rollable loot items. Given that at the time the bird was worth ~2m gil, I sold it to help fund our FC house. I guess I must've been exceedingly lucky to get it. I haven't seen another one since.
As an aside, due to the unhidden maps, peisteskin maps doubled in price on my server. x_x
Friends and FC and myself have been doing maps since they came out. We saw 2 minion drops in half a year... now like last week... we had 4 or 5 of them drop in 2-3 days... so 3 of us got the blubird and 1 got the bulb.