Explain to the kid that this is something most people cant afford/wont spend money on, and that your hard work in life has got you there. If they are too immature to understand that then reconsider. If they understand that, then tell the wife that this kind of experience may inspire the kid to work hard enough in life to achieve such experiences themselves.

Last year, with my 14 & 15 year old travelling with my wife and I, we were in premium economy. Upgrades at airport counter were available to CW. We were seriously considering it but the kids talked us out of it since they perceived it to be poor value for a 7hr TATL and came up with examples of other things we could do with $2500