I really want to go to this concert, and I'm feeling like I'm going to make my girlfriend buy the tickets.
Why do you feel you need to force her to buy the expensive tickets?
Because they cost around my weekly income and I really want her to take me.
Making your gf buy expensive concert tickets just because you can't afford them is forceful and imposing on her. If she wants to get the tickets then let her, otherwise find a way to make more money so that you can afford them.
It's not like I would force her against her will. If she doesn't want to buy them then that's on her.
Well you need to approach a situation carefully. Just simply ask her if she would be willing to buy the tickets so you both could have a good time. If she's not interested then you should drop it.