Sure! As for cost... well... it really depends on what you get. I'd say a decent starter is cost of the van + 30-60k for the build out (including labor).
AT&T has an unlimited 4G for business plan that is only about $100/month. They accept 'consultant' as a business (I went into a store to simplify the process of setting up the account). Get a mifi (Netgear M1)... it has 2 ports for a mimo antenna. Get an omni directional antenna and the shortest cables you think you need. That should get you coverage in most places. I've taken my daily zoom calls on the tops of mountains in the middle of nowhere. There is a newer Netgear 5G mifi out now too, but I haven't looked into it yet as I'm ok on 4G and 5G coverage, especially in remote areas, isn't that great yet.
I spent 2 years on a small motorbike going all through super remote areas of Vietnam, Cambodia and Laos and living out of hotels and short term rentals. Living in a van is easy after that. =)