Powder coating is a barstool to get off, and will be expensive to get shot blasted.
Wire wheels/flap wheels on a grinder just smear it around so your best bet would be to have a very large bonfire and throw the bull bar on, or flash over it with oxy acetylene
Your choice after that as to whether you go with paint or powdercoat, I would agree with Matthew2riches and paint it.
From talking to local body shop, it needs an acid bath to strip the powder coat off and then painting/galvanising/whatever. He said they use a place in Preston, but no luck phoning them yet. I've started removing damaged areas with a knife and treated the rust. I'll probably just Hammerite the affected areas. Looks like anything else may cost to much at the moment.
Hot air gun helps