its either alright or it isnt!
£500 for something thats ok, very strange.
oil pump could be on its way out, and if it fails when its running, and this you will not know as your light is on all the time, will not repair for anything like £500.
if its just the pressure sensor get a new one in now.
could be idling to low, but i doubt it.
you are playing with fire, and if you dont get it sorted you wil get burnt, very burnt.