Assuming you are running on road over longish training runs, two things matter, the fit on your foot and the control / support required by your gait / running style.
Going to a pukka shop for assessment is safest but can be very expensive. A cheaper alternative is to carry out a wet foot test at home as advised by various running sites, also look at the wear pattern on existing trainers. Both should give you an idea of your gait. Most people overpronate slightly and are suited to stability shoes. You may or may not be one of them.
Visit a cut price outlet that stocks end of line / last season decent branded shoes, I use TK Maxx but JJB / JD sports also stock decent stuff amongst the chaff. Find a brand /size that fits your feet as last shape and published size varies between brands. Check that manufacturer’s web site for their comfort / stability / motion control shoe ranges. Choose a shoe from the range that suits your gait. Don’t buy the wrong type just ‘cos it’s cheap, stock changes, you don’t.