Well, 1750 is not a bad time to pick to time travel to go see a little of the Western Arts Music canon! I'd pick about 1730 myself but still, not a bad choice.

"Concerts" as we enjoy them today (buy your tickets at the box office, stuff your children (if you have them) into velvet dresses and wee little suits, and then sternly sit through a night of Culture Goddamnit) weren't totally around yet. But here's 3 major ways you might get yourself some art music in 1750:

Opera: for the opera, if you were rich-rich you wouldn't have tickets, you'd have a box which you owned for the season. So you just went if you felt like it. If you were middling-rich you would send a servant in advance to go buy your ticket at the theater and save you a seat (numbered seats matching to a ticket had not been invented yet). You could also just buy your ticket at the door and take your chances. You might also be on the "free list" the (you guessed it) list of people who the impresario let in for free, which was prostitutes who'd be working the floor area usually, but that varied from house to house, gondoliers in Venice were customarily on the free list as well.

The opera house would also often have "benefit" concerts, these were concerts for the star castrato/prima donna to make extra money by doing a solo night, and you were expected to buy a ticket for this even if you owned a box, as it was for the guest singer to make money. I'm not sure but I believe some of these tickets were bought in advance, judging from the wording on newspaper announcements for them, but of course you could also buy at the door. There were also more conventional benefit concerts for charity, and then again it would also be considered tacky to not buy a ticket even if you had a box. This group did a lot of charity concerts in London about your time.

Private concerts: these were very popular, and held in some rich person's home, and you wouldn't have a ticket because you were a guest. Also free food and stuff. Obviously the best way to go to a concert at your time but tricky to get an invite if you're a time traveler! A pretty serious source of income for itinerant musicians for a long long time in Europe.

Subscription concerts: These were up and coming in the second half of the 18th c.! Okay, the basic idea you need to think about for making music at this time is that it takes a significant amount of capital to start up, so people all buying their tickets at the door isn't workable. The opera house relied on its rich-rich box holders paying for their whole season in advance, as you then took that money and made the scenery, and hired the singers, the musicians, the librettist, the composer, etc. The people buying tickets at the door were nice and all but you can't run an opera on that. You need money up front. (And don't think you can roll over the last opera's profits, opera rarely turns a profit. The impresario pretty much started from scratch each season.)

Now, let's say you're a composer, and you just want to play a few concertos for a hundred people or so. If they pay you when they get there that's no good, as you don't know how many people you're going to get, and how will you rent a space and pay your musicians? Enter the subscription concert, where your fans could subscribe to a series in advance, get the tickets, and then the musicians could be paid and the hall rented before they show up. This was a way Mozart aired some of his music. Subscription concerts were a transitional thing between the traditional royal-patronage system for composers and musicians and more modern models of musical economy.

Let me know if I can expand on anything!