Wheelchair transport in London?

jand23

hello everyone! I hope someone can help. We need to arrange transport from Gatwick to liverpool street station next week. I just found out there will be strikes and the trains won’t run .
So we are looking for a transport company. we need a big car with room for two wheelchairs, one electric and one manual. 

It seems impossible to find under 450 pounds..! It was easier on a small island in greece than in big London.. 

does anyone have advice on who we should call?
thank you!