http://www.cabrillo.edu/~dambrosini/188Web/classsessions/merchandisesales.htm
Grabagun is operating under a misconception, as far as I understand things.
(Someone with more legal savvy, please feel free to correct me.)
If an item is ADVERTISED at one price, then the business is obligated to SELL at that price to anybody who wants to buy it at that time unless they choose NOT to sell it at all. They can change the price
with proper notification under the uniform commercial code.
Since the business has been notified of this problem on more than one occasion and the issue still persists, then this MIGHT come under "bait and switch" tactics.
Since Grabagun is also a brick and mortor store, from what I see, if you are local one option would be to print out the page with the associated price, take it to the store, and conduct business there with that page as proof of their advertised price. If they sell, then they have to sell at their advertised price.
Another avenue MIGHT be to conduct business over the phone or by email. Some people choose to conduct business over the phone because they do not wish to put credit card information onto the internet. Some business will do business this way. If so, then you can also corner them into the advertised price.
And finally, you can attempt to press the issue through customer service the same way.
THAT SAID...you have to ask yourself what the cost of all this is to YOU. (Or whomever else may wish to deal with them.) It takes time and some amount of aggravation to wade through all this.
Frankly, I like the fact that you simply took your business to someone else. Personally, I'd also take the time to call Grabagun's customer service number and ask to speak to the owner/manager. Then explain to them exactly how this unresolved problem cost them the loss of an otherwise guaranteed sale of X amount of dollars (you were literally a click away from confirming the sale when you found the price discrepancy) and that it is also costing them additional losses that you know of from others also unsatisfied with their website "bug".
But that's me.