First off, I'll ask a question

I heard that vinyl pressing is relatively cheap, and affordable. Which is why a lot of underground grindcore and death metal bands usually only have their EP's pressed on vinyl (So I've heard)

But does anyone know any good services that press vinyl's (About 50-100 copies) and how much it will be? (Tried Google, most sites don't even give a ballpark estimate, or they have confusing rates)

It's just for the hell of it, when ever I do a decent demo sometime in the next 5 years when maybe I can play a real instrument other than using FL. If CD's are cheaper than I could go that way too maybe

Vinyl pressing is more expensive than CD's actually, especially if you're only going to press 50 or 100. The less vinyl you press, the more expensive it will be, because it will be like a limited edition. Also the so called glass-master of a CD is cheaper than the lacquer mastering of a record.
If you still like to go through with it http://www.urpressing.com is a good company for pressing them. They are reliable, quick and have great quality vinyl.

Having said this, don't forget to think about the logistics of pressing your demo. What's the standard use of a demo? Getting your music out to the public, but also promoting your music for venues, labels, radiostations, bookers, distrubutors, etc. How many people do you know, who actually still own a record player? (I have one, but I'm quite picky when it comes to sound and music) And how many of those are under 18, sad to say, still the future of our planet and a big part of our audience, as musicians.
Another important thing to remember is that most of the people who work for labels, or as bookers, etc, etc, are major league assholes who don't care about your music at all, they just want to make money. Their time is valuable to them, and I can assure you that they'd rather get a CD in the mail, which they listen on their computer, home-stereo, dvd-player, wherever, than that they receive a record (which will also cost you a lot more to send, because it's pretty fragile) and have to go look for a record-player.

Good luck with everything, and as always I'm curious about the result.

having recently released a recording, i can tell you this:

Cheapest: CDR's (up to 200 copies) with hand made covers AUS$2 each

Midrange: Pressed CD's (minimum 500 copies), about AUS$2.20 each with jewel case and 6 panel REPLACE. Slightly more expensive for a digipak.

Expensive: Vinyl. Sadly.

Most vinyl questions can be answered here:
http://www.zenithrecords.org/
or here
http://www.piratespress.com/vinyl.html


Feel free to PM for more details. Or reply here.