are the general differences between the bodies/necks of a guitar that costs, say, $300 vs one that costs $500 substantial enough to warrant going the extra $200?

i'm gonna replace the pickups no matter what guitar i buy.

The body/neck is a large factor in the tone/sustain of an electric guitar. It's rather important, but it's hard to answer your question right off the bat without some specs/info on the guitars you're comparing. Mind posting some?

i'm thinking like the jackson mgs, the ltd m's, and the ibanez rgs. that kind of style.

Well, I'm probably not the best person to answer your question (not my area of expertise), but I own an LTD mh-50, It's a rather low-end guitar in comparison to alot of the models out there... But if this is low-end, I'd love to try out a more expensive LTD/ESP guitar. The mh-50 sounds great for what it is, and it feels incredible... Very natural to play.

I haven't tried the higher-end LTDs, but if they retain the same sound/feel as this one and merely improve on it, I wouldn't be able to reccomend them enough. Can't say for certain though, so don't take my word for it.

Was there a specific comparison you were wondering about, eg. what kind of wood or neck joint to go with? Or just wondering if there was much difference in general?

just a general difference

Well, it is a very important factor. If the body/neck are shit, but you've got great pickups, it'll probably still sound like shit. Great electronics won't save a crap guitar, pretty much.

ok thanks

Go for Jackson. Shit Jackson sounds better than shit Ibanez.

Well I own an Ibanez SZ520 and I like it mucho. Sounds good and I've yet to change the factory pickups. Comfy as all hell too. I like it more than the crappy Jackson I used to have as well, but each to his own.

That's the thing. Everyone's gonna tell you something different regarding what guitar to get. Just gotta try 'em yourself first.

I have/had guitars from Jackson, Ibanez and an LTD H-207. The best for playability is the Ibanez. Stock pickups aren't great on an Ibanez, but if you're replacing them anyways, go for the RGs. Ibanez are notorious for being fast guitars.