these days a rough price for a litre of metallic base would be around £40+vat per litre, thats what i paid not so long ago for my mallard green anyways
then theres the lacquer, which as said above can vary dramatically depending on the branding, but luckily my painter is happiest working with a relatively cheap brand so cost me about 70quid for 5 litres.
then a high quality thinners could set you back about £30 for 5 litres
of course its all dependant on how much is actually needed, id guess for a single side of the car, a litre of base would be plenty, as thats 2 litres when thinned. then of course you wouldnt need a full 5 litres of lacquer or thinners, so could buy these in litre tins instead to reduce the cost
id hazzard a rough guess, and i emphasise the rough bit, that actual materials used would be around £100