"You're too expensive" = "you're too expensive for me"
Just remember that when you hear this it isn't a complete sentence. The full sentence is actually "you're too expensive [for me]".
And that's ok!
There are all kinds of businesses they can purchase from. But since that isn't you try to think of ways to build on their comment. Since they took the time to comment make sure you respond.
Reply in a positive and productive manner. Tell them thank you for your input, offer advice on how to receive a discount code for your store, or whatever you want them to know.
Respond simply to comment. Commenting is a super positive action on Facebook. When they comment it shows that post to their friends (many of their friends if your group is public, or only to friends that are in the group if it's private). When you comment, it possibly helps increase your views of other types of members.
Takeaway:
Don't let negative comments go to waste. Defend yourself and communicate with members.
Commenting is organic reach.