I have been riding for more than 60 years and my bike(s) have only seen the inside of a bike shop a handful of times.
Park Tool web site is wonderful for any level of mechanical competence to learn a fix-it skills. Don't be ashamed to watch a video (and there are lots) multiple times until you understand the process. Sometimes just an adjustment, sometimes replacement. Rarely can a problem not be diagnosed and solved. Your limitation is likely to be: do you have the tools for repairs. Your budget might be more strained with buying tools rather than getting something fixed.
Also, if the axle seems to have movement that you can elicit by just pulling and pushing the crank arms, you might not have to pay for parts, just the labor (which, admittedly, can be exorbitant). Ask this "mom's bike shop" what they charge for a bottom bracket maintenance. Might not be so bad...
Suggested reading: https://www.parktool.com/en-us/blog/...bottom+bracket