Sounds to me like the crank needs to be taken off, cleaned and inspected. If all races, bearings, threads etc are in good condition then they can be regreased and reinstalled.
Cross the bridge of worn/broken parts as you find them.
It's not a big job if you have tools etc.
However, if it's not your cup of tea then the bike shop is your only option.
Are you happy to strip it down yourself?