Ok, so that is a really fun and neat idea! I would do a little research on pillows, particularly if you can find anything custom. Looks to me like between $25 and $35 is the biggest price pool.
There are lots of pricing formulas, but the one I like is: materials+labor (total of your hours spent by your hourly rate)+expenses+profit (what you want to make on each piece)=wholesale x 2= retail. (this came from etsy)
I think you can set a general price for one, two or three pillows. But, since this is a custom thing, depending on what you end up making, you may have to adjust pricing accordingly (and I mean don't undercharge yourself if you go above and beyond and make a specific shape that is really complicated, or add other material embellisments that come out of your pocket)...
Good luck, this is a clever idea.