If its a front wheel drive car the front tyres tend to get a lot more wear as the rear are just trailing really, partly why people sometimes rotate/swap their tyres around,
Check the specifications of the tyres you already have, it will read something like 255 (tyre width) /30 (sidewall as a % of width)(/R18 (wheel size in ") we don't need to dwell on the details but that's the info you need to get another tyre that fits.
You do a get a wide budget of tyres and will likely find cheap ones for 40-60 for most basic cars, but you can easily pay 100s for high end ones. I often use somewhere like BlackCircles where they have a network of garages to send the tyres to and fit for 'free' but your purchase price obv takes that into account, but I think my local indy place charges £15 fitting?
I've seen different setups where they trolley jack your car up outside then take the wheel into their garage to fit or they've had a proper car lift they drive it onto, often if they also do exhaust/MOT work etc.