I don't think it works quite like that. A recording is a chain, and a chain is only as strong as it's weakest link.

A $5000 preamp won't help a $25 Radio Shack microphone at all. A $5000 microphone won't sound good through a $35 preamp.

In all things, there must be balance. Just my .02.

If the $100 mic is a Shure SM57/SM58 then spend the $500 on the preamp. If the $100 is some POS cheap chinese condenser then you're screwed.

Buy a good pre-amp and a really cheap mic!
Then you stuff the mic into your coat pocket and go bank heisting for some more cash.
Then you get a good micro. If you are lucky, it has become a valuable classic by the time you get out of jail...

Nah, ...just kidding.
The thing is, if you buy one good and one bad it wouldn't be reasonable, because the result is below average.
If you actually want to get into audio recording and do usable recordings, maybe earn some cash with it ( and obtain a good name from the start ) ,
the way I would go and I actually did is safe more cash to get decent sounding gear. It will serve you much longer and will be in use for many years.
If you want to sell it, you get some money back. With the cheap stuff that will be much less.

Now, with some effort and research, you will find mics and amps that are reasonably good and not too expensive.
I am sorry, that I can't be of much help, here. The first gadgets I bought are looong off the market.
And the 1st microphone is a MD 421, which I still use in my studio, but I would not count it under good and cheap...
I had to repair quite a few TV sets and mount antennas in the '70s to lay down the cash for it.

Anyway, get the best pre amp you can afford and maybe lease a better mic. If you do this only for fun, it would not matter what you buy,
but 600 $ is a fair enough amount to get both in usable quality.
Maybe you want to present some eqipment of your choice here and let the chaps comment on those.

You can't hide a bad mic. However, you can use cheap preamps effectively. Cheap preamps don't have much headroom and sound bad in the upper (nonlinear) parts of their range. Keep the gain low and keep them as far away from the red as possible. Yes, the signal to noise ratio is higher, but the transients will be clearer. And I'm afraid that even $500 qualifies as a "cheap" preamp. At least that's how I regard my FMR RNP and Brick. They are OK if you baby them.

BobRogers, post: 359697 wrote: You can't hide a bad mic. However, you can use cheap preamps effectively. Cheap preamps don't have much headroom and sound bad in the upper (nonlinear) parts of their range. Keep the gain low and keep them as far away from the red as possible. Yes, the signal to noise ratio is higher, but the transients will be clearer. And I'm afraid that even $500 qualifies as a "cheap" preamp. At least that's how I regard my FMR RNP and Brick. They are OK if you baby them.

Using ANY piece of gear no matter the price requires that it be used within the constraints of its design and abilities. Doing so will usually result in decent sound no matter the cost.
Balance in quality is always a fair way to assess the gears abilities to perform to a certain level. Again, this doesnt have a LOT to do with price.
The used market is full of decent gear at half of retail, and a $600 budget can get you a nice setup if you are patient and research dilligently.

An FMR RNP and an ADK Hamburg mic is around that range used for sure and both are decent pieces.

Thanks for the responses. What I have now is a Presonus Digimax D8 and an AKG Perception 200. I also have an SM57 that I've used in conjunction with the AKG mic and also with recording acoustic guitar.

Two out of three of those are perfectly adequate for basic work-and the SM57 is a world wide standard. If you want to dump $500 then replace the AKG 200 with an AT4050 or a pair of NT55's. Otherwise perfect your microphone positioning.

Thanks. It seems like the AT4050 is a well liked, good bang for the buck, versatile mic according to multiple forums.