Mobile/portable AP for internet access for non-profit active in emergency and disaster support

Hello together,

while my education did teach me some foundations on networking and I like to dabble a bit in R&S, I am no networking professional. This is why I am hoping you could provide me some hints. (And please excuse my language mistakes, English obviously isn't my native tongue.)

The chief of a growing regional non-profit in Germany that provides psycho-social support to survivors of emergency situations recently discussed their plans to expand their ability to respond to situations of mass casualties, disasters and catastrophies with me. They work closely together with government institutions tasked with emergency response.

For legal reasons they don't have access to government radio and communication channels for emergency response, but have been recommended to try using commercial mobile networks for the time being. Securing internet access even in remote locations (for a densely populated country like Germany) would fulfill a key need to organise their operations.

While they do have qualified technicians in their organisation, creating an ad-hoc mini-WISP on the go in some tent, impromptu-building or random public building for their senior staff creates some difficulty for them.

Many of these places do not have the ability to provide, say, usual ethernet infrastructure immediately, and, as stated, the government emergency management networks are not directly accessible to them. They plan to acquire portable UPS devices, so power should be there for an initial period.

I told the chief that I would have a look and try to find about internet for their core lead staff, amounting from 5 - 10 people, working together with and coordinating the actions of potentially several dozens of other team members. Their organisation is growing, and their work is appreciated by the government agencies and offices tasked with emergency response, with whom they work together closely. But as stated, for legal reasons they can't use the government channels.

Apart from voice and e-mail, the access to the orgs internal web apps would be considered key for making their operations more efficient and responsive.

Two-Way-Satellite-Internet has been on the table, but is seen as very expensive in hardware, subscription and data (especially up). (Are there cheaper ways to realise this?) Most of the area the non-profit operates in should be covered by at least one of the three German mobile network providers, Deutsche Telekom, Vodafone Germany, and Telefonica Germany/o2.

I am superficially aware of products by Icomera used by the German national railway company (Deutsche Bahn) and the long-distance bus Flixbus that use all available mobile networks to provide on-board wi-fi. I tried online-windows-shopping for any APs that provide such capabilities, but my google-fu failed me due to my lack of terminology and certainly foundations in wireless networking. Are there commercially available "multi-homed" mobile internet products affordable for a non-profit?

If there is no way to realise something like that at a reasonable price (let's say, less than a few thousand €) and me rushing to learn BGP, is there a preferred way to use three provider-specific mobile APs together, or should they consider a combination of "satellite down, pigeons up" and eat up the latency issues?

Thank you.

TL;DR: Non-profit wants to have internet access on short call in new / remote places, but can't afford a reverse, "fiber-planting", backhoe (send the backhoe in, and fiber grows immediately in the earth). What can they do?