I don't know where you heard that, condenser mics almost never need a high gain preamp. They also tend to be too detail oriented to sound good with harsh vocals. The two mics that keep coming up in those conversations are the Shure SM7b and thr EV RE-20. Both of those need a lot of gain.
Really, if you are just starting out, an SM58/57 will work fine. Since those are usefull in so many other applications, they are never a bad investment. ( especially if you buy used)
Do you hqve an interface with mic inputs? If you do, you probably don't need a separate preamp.
For the most part, any mic you can get your hands on will be fine. When people talk about "the perfect mic for metal vocals", they are talking about mics that are not that much better than anything else. There are also dozens of vocal styles that all fall under the "metal" heading, and that factors in as well.
If you already have a mic, just use that until you outgrow it.