It doesn’t really matter what you do, it’s going to be pricey.
I work away a lot and I have a Mikrotik SXT-LTE that I suction-cup onto the outside of the hotel window and a flat Ethernet cable that I run in to the PoE switch. And I then plug my PC into that, and a UniFi Flex-HD if I need WLAN.
Being from Eastern Europe where 4G is widely available and rural broadband is literally non-existent, Mikrotik offer a wide range of options. The SXT-LTE6 kit is £150, the LHG-LTE6 kit is £180, wAP AC LTE6 is £190, Chateau AIO LTE6 is £225 and the Audience AIO LTE6 is £265. They’re all based on the same LTE6 Mini-PCIe modem card which is £100 if you want to upgrade an older unit. They’re all good.
A decent Huawei AIO router will be £120 plus, say, £40 for a pair of directional antennae, and it’ll be £100 to mount and cable those in.
Teltonika is also excellent, and would be similar money to the Huawei plus antennae.
For me, I would get a specialist in, get a site survey done, and spend the money once for a proper solution that works rather than mess about with something cheap where you spend more, just in 2 or 3 chunks because you didn’t do it right the first time.