As suggested if your cellphone works where you will be for those 3 months, that is probably the best option
No other devices to buy
Just add hotspot service to your cell pLAN, turn off when you return home
Or
Upgrade your phone and your cellular plan
Assuming this is work related ? You can add it too your expenses when you file your taxes next year
Also assuming this is work related, what ever the expense, is better than not getting a paycheck/ income for 3 months
And it is a business expense tax deduction
If it's for personal use pleasure, you have to weigh the cost, against the entertainment value, and unless you are on free land with NO camping fees for those 3 months, the internet data service is going too be one of your lessor expenses compared to campsite fees, travel fuel etc..
You have to look at the big picture,