Hey man,
since your budget is below 1k, and youre looking for a Metallica-type tone,
and ESPs and Gibsons are typically very expensive, unless you score a good
deal here on soft.com, I suggest you consider either getting new pickups for your
Eric Johnson strat, or if you don't want to, you can also consider buying a cheap
Squier Strat or cheap Ibanez or Epiphone V or smth and modding it with your own
high-gain pickups.
The Seymour Duncan Invader is a popular and very reliable high gain pickup, and
is the preferred choice of many metal guitarists. You can also try the Black Winter
by Seymour Duncan or even the JB, to a certain extent. Di Marzio also puts out some
good high-gain pickups.
But in actuality, I think the main problem here is your amplifier. You can't use a Vox AC15HW and expect to put out a Metallica tone. I love Vox's for their cleans and overdriven tones, but then again I don't play Metal. If you're looking to play metal, a Vox is not your best friend, because its known for its signature chimey, bell-like tones, not blistering low-end which is what you're looking for if you want to get a Metallica-type tone.
I suggest swapping your amp for a Marshall or even a 30w Ashdown Engineering Bass amplifier (we all want Mesa-Boogies but we cant afford the 1,500 price tag), and buying
a Sans Amp GT2 guitar pedal. The manual that comes with the pedal even has a section that shows you what settings to use to get a Metallica tone. It costs about 280 brand new, but i think you can get it here on soft.com for about 180-200.
All in all, getting a cheap guitar to mod, a new amp and a Sans Amp should help you get that tone. Buying an expensive Ibanez or ESP and using it with your Vox isnt going to yield the results you want anyway, so really consider swapping your amp and keeping the project DIY by sourcing for your own items.
Good luck