A) Dont talk in caps
B) Varying amounts--bust very expensive depending on bandwidth usage
C) Double double post--you just look more annoying than you are (which seems hard to be) but people just feel the desire to ignore you more than to answer you.
IT DEPENDS ON A LOT OF THINGS. IT COULD BE FREE, IT COULD BE THOUSANDS OF DOLLARS. YOU HAVE TO BE MORE SPECIFIC. THE SOFTWARE ITSELF IS FREE, BUT YOU NEED TO HOST IT SOMEWHERE. IF YOU HOST IT ON YOUR OWN MACHINE THEN THAT IS FREE AS WELL. TYPICALLY YOU'LL WANT TO HOST IT ON A SHELL ACCOUNT, THAT CAN COST ANYWHERE FROM $10 TO $100 A MONTH. A SHELL USUALLY LIMITS YOU THOUGH. YOU ARE LIMITED TO A CERTAIN AMOUNT OF USERS AND A CERTAIN NUMBER OF LINKED SERVERS. SOME PROVIDERS ALSO DISALLOW YOU FROM HAVING CHANNELS DEDICATED TO WAREZ, MP3S, OR PORNOGRAPHY. IF THAT ISN'T GOOD FOR YOU THEN YOU HAVE TO PURCHASE A DEDICATED MACHINE OR A COLOCATION. THAT CAN COST SEVERAL THOUSANDS OF DOLLARS A MONTH.
ADDITIONALLY IF YOU WERE THINKING YOU WANT A DALNET, UNDERNET, EFNET, ETC. SERVER, MEANING LINK TO THEIR NETWORKS, THAT'S DOUBTFUL. 99 OUT OF 100 TIMES THEY ONLY ACCEPT LINKS FROM COMPANIES SUCH AS ISP AND WEBHOSTERS, NOT FROM JUST SOME GUY OFF THE STREET.
FINALLY, RUNNING A SERVER IS NOT EASY. MOST IRC SERVERS ARE RUN OFF OF LINUX MACHINES WHICH MEANS YOU NEED AN INTIMATE KNOWLEDGE OF LINUX. YOU ALSO NEED A GOOD KNOWLEDGE OF NETWORKING SO THAT YOU CAN ISOLATE AND DIAGNOSE PROBLEMS THAT MAY ARISE. YOU ALSO NEED A VERY GOOD KNOWLEDGE OF IRC. YOU NEED TO KNOW WHAT AN IRCD.CONF IS AND HOW TO USE IT, YOU NEED TO KNOW HOW TO MANAGE A NETWORK.
SEE HOW ANNOYING READING A POST IN FULL CAPS CAN BE? NEXT TIME YOU'RE TEMPTED TO POST IN FULL CAPS, REMEMBER THIS.
well how do i make my own then???
the answer is in your question.
Download the software, install it on your machine, or install it on a shell account you purchased. Read the documentation it comes with, and do what it says.