If I buy a ticket, how much will it cost? 

If I'm going to buy a ticket, how much does it cost?

Check out some information on first and second conditionals. This site seems to be pretty good:

http://grammar.ccc.commnet.edu/grammar/conditional2.htm

Basically, first conditional is constructed like

if [present tense], [future tense]

...and second conditional is constructed like

if [past tense], [phrase using would / could / should]

So, you could also say "If I bought a ticket, how much would it cost?"

Also, don't worry about third conditional for now. It's very complicated.