Thanks guys what sort of prices should i be expecting for this???
Will you be stripping the car out yourself?
You would need to remove all of the interior (anything fabric based or that would burn or be burnt by stray sparks and move clear any brake lines/fuel pipes from beneath.
If you are having the whole thing replaced, it will obviously be dearer because there is a lot more involved but if you are going down the route of cutting what you need from the new pan and welding it in then it will be considerably cheaper.
Bare in mind that depending on who does the job, you may need to specify that you want a corrosion resistant paint (like Zinc primer) in all of the seams like the toeboard where the pan sits over the top and that you want the pan to be butt welded in and not just laid over the top as this will cause all sorts of problems down the line.
The best bet is to let someone who knows mini's do the job and preferably someone who wants to make a nice job of it. i have seen some real horror stories done by general welders who think that tack welding a piece of steel over the holes and then covering it in underseal is good enough.
it would also keep the cost down if you ask to have it back unpainted (well in primer would be good) then that way, you can do the refinishing yourself to a standard that you would be happy with like sealing it up, stonechip etc
as for cost, don't expect it to be low for a decent job. If the price is low, it will usually reflect the quality of the job.