I found it remarkably difficult to come up with a verb that has this kind of specific meaning.
There is no verb form of the adjective available, which would be ideal.
However, in thinking of something that is at first available to only a few, but then becomes something routine or common, one verb is commonize:
: to make (something) common, standard, or universal
// Because the book is considered to be so highbrow I wanted to “commonize” it a little bit. I didn't want to fall into the trap of being inaccessible.
— Kari Skogland, quoted in The Calgary (Alberta) Herald, 23 May 2008
// We have to reuse and commonize what has worked and what has been well received by the customers.
— Birgit Behrendt, quoted in Automotive News Europe, 13 June 2005
Ironically, it's not a common verb, but your sentence would become:
Travel was for the wealthy but the introduction of the package holiday commonized travel.
Other less satisfactory verbs I had originally considered included disinhibited, unleashed, derestricted, liberated, unbound, unchained, freed, and unfettered.