For the last eight years I've gotten on extremely well with Regal Paints
It sprays and rollers on really well; have just sprayed a load of steel fabs today with black gloss topcoat on to corrosion resitant grey primer from yesterday and this afternoon I'll be rolling some of their corrosion resistant primer on to MDF boards for a panelling job in our house..
The Primer and top coat both thin with standard/32/cellulose/xylene thinner, and use the drop down arrow to see the price per 20 litre can.
If you go high build vinyl, generally used straight onto galv, don't get it from Brundles, theirs is utter crap now, even the Rourkes vinylast that has been their better quality option has gone down the pan recently. They seem to have forgotten that there should be vinyl in it. Recently had 60 litres of the stuff, not a happy bunny!! As above Manor coatings is reliable stuff. Vinyl not good on bare steel without a decent primer.
If it's a bare steel job I use Lechler technogrip. Very good stuff and will adhere to pretty much anything.
But this is going to be one of those threads where you get so many different recommendations you wish you hadn't asked