Greetings, question about getting design files

I am new to the 3d printing game. I am wondering how people generally acquire 3d printing design files. Mainly from websites where you have to pay? I have no problem paying for design files, but am just wondering what this process is like before I invest in a printer. Here are some issues I am expecting may occur:
-Difficulty finding quality design files that print well
-Lack of many good 3d printing designs out there
-Too expensive for good designs
-Cost of designs really adding up (I am hoping to do quite a bit of 3d printing, if I have to pay a lot for all of the designs does it get really expensive? I am already spending quite a bit on the printer and cartridges!)
-Lack of many useful designs (not just artsy designs but things I can print that have a use to them)

Thanks for replies!