They're not the President. They're not even government officials. The Secret Service has no business giving them personal protection, free or otherwise.
This is the reality of the job. There are any number of people that would like to take out Trump and/or his family as a result of Trump's service to the country. Securing people traveling outside of fixed secured locations is very difficult and only getting more so with modern communications, drones, etc.
My only issue is that those being protected need to understand that they cannot go wherever they like and they need to limit their travels to what is practical and not outrageously expensive to secure. There are limits. They also need to limit how often they take these sort of trips. This compromise comes with the job their father sought and won and that should be understood as one of the consequences of it.
So thinking about it, what should really happen is an overall 4 year budget should be setup by congress for this purpose and the people being secured need to live within it when used for recreational purposes. If they want to travel more than the budget allows then they can kick in what goes over the budget.