Yeah, no one wants to spend money on expensive BBs, but we do, because it's a bad place to scrimp. Once you've experienced a gun with BBs jammed in the barrel, you'll pay extra not to ever have it happen again.
Luckily, in these days, it seems most BBs are good enough, and it's only the very cheapest that are still rubbish. Those ASGs are probably fine...? If you can afford to buy in bulk then Warhead will be good, and you'll be playing very little more per bag.
You definitely need to check whether your local site insists on bio's though. You'll not be allowed to play if a diligent marshal finds you're using non-bio where bio have been mandated.
Edit: in fact Warhead BBs are the same price for a 1kg bag of non bios, though I didn't compare the postage.
It's sometimes worth trying eBay for somewhere with free p&p.