Write it down. Be honest.
"I "max out" my 401k"
"the best cable package just costs a little more"
The difference between a $70 per month cable package and a $100 per month package is not "a little more", it's 42.8% more, $30 more per month, $360 more per year, etc. That's not to say that your family cannot choose the $100 package -- it just means that you really understand the impact to the household budget.