I bought a huawei 4g mobile wifi device off ebay for about 25 quid earlier this year, and have a 3 sim card (the huawei device is branded 3 anyway, but they don't lock them) with 20Gb/mo data for 15/mo but you can get cheaper contracts since you don't need that much data. I run it from 12v, pretty sure you could mount it on an electric weelchair..