I have something to tell you of utmost importance. Some things in life aren't cheap. Good tone ISN'T.
I am not slandering those with a small budget, but if you stick with it, you will pay.
Those solid-state (also know as transistor amps) are not going to make you sound like your rock 'god'. I don't care how good you are if you are playing on a Marshall M10 watt combo, you won't exactly sound like a professional. WATCH THIS STATEMENT: You may PLAY like a professional, but it isn't going to SOUND professional (as in studio, or gig, etc.). Don't get me wrong, paying like a professional is definitely an achievement and something to be proud of, but so is good tone.
(Trashed kicks the dust off of his boots and continues)
Are tube amps the end-all for tone? No.
Personally they are for me (I have 19 quality tube amps), and I love the suckers.
Do you need tubes to sound like a 'professional'? No.
If you are on the way up, an amp is the core of your tone. $400 used gets you a great combo in the right market. I am referencing a Peavey 6505+ combo, Marshall DSL40c combo, Fender Hot Rod Deluxe combo, etc., but there are tons. That $400 will be WELL spent.
Lets talk about guitars. Your $100 Squier Strat, is a viable instrument with a little work. Your $100 Epiphone LP Special (IMO) is trash-can bound in time. It depends on what guitar to a degree, but at that price the quality is generally pretty low across the board.
So Trashed - WHY do you want to spend a little more on a guitar?
There are a bunch of reasons. Typically mid-level instruments stay in tune better, are of higher quality regarding fit and finish, the fretwork is notably better, the hardware is a little better. They will just feel better in your hands, if you are transitioning form a cheap guitar, and you play a mid level guitar, you will feel the difference right away. It isn't something I can really describe, its just a vibe.
I am going to stick to the sub $400 used budget. Ibanez RG's (without tremolos), Epiphone Les Paul Standard, Fender Mexican Strat. They will all play well with a little set-up, and sound much better. If you are obsessive, you may want to get a new nut fit for it, maybe a fret-level and crown. However for me? I haven't done that on any cheap guitars.
Is $800 a lot to invest in a past time/hobby? To me, not a whole lot. I can probably think of a dozen more hobbies where you invest more in mid level equipment. Also for most of my readers, they are beyond the entry phase to be researching.
Pay to Play.
*I have a bunch of disclaimers here. The guitars and amps I referenced are just really common guitars and amps that you can find anywhere. In most of those cases they can be found cheaper. I posted those for a broad audience, a basic 'metal' rig, a 'rock' rig, and more of a 'clean' amp for other things. However, they are ALL gig-worthy.