Competitively priced compared to what... Clubman Bay Rum ($7 @ Walgreens for 12-oz) or Guerlain Vetiver Extreme EDT ($86 @ Sephora for 4.2-oz)? :D
Until we have something we think is acceptable, I don't see how we can we address the cost/pricing issue in any more detail than a ballpark estimate? However, regardless of the scent, we/you/Noam can work on choosing the bottle(s), label design(s), etc. and get those costs reasonably identified. Once the scent is chosen, then the ingredient costs will be fairly easy to identify. I do know that many of the EOs vary widely in cost from vendor to vendor and often fluctuate with availability, etc... so your margins need to be sufficient to cover those fluctuations without constant price changes.
I think the "percentage" would best be determined after we know whether there are sufficient sales to support doing so. You'll certainly incur some "up front" outlays to stock bottles, labels, and ingredients in quantities sufficient for our needs. After we see how sales go for a while it might then be appropriate to consider a "kickback" to the site.
Just thinking out loud, and speaking only as a member, I'd like to suggest you/Lynn consider "payback" to the site being, at least in part, fulfilled by you donating more (than you already do) of your products to the monthly giveaways and regional get togethers. JMHO.