You need sun glasses of some kind if you plan on riding in the summer in the day time. If you ride a road bike and tend to put quite a few miles a week on it you can try glass over sun glasses. What you need is something to block dust, dirt and sand from getting behind the lens. Yes you have an investment to think about if you decide on any of the wrap around styles. No it isn’t than bad if you decide flat sun glasses will work and you can get glass over sun glasses for $15 to $20.
I put on 5 to 8K miles a year and when I don’t get coverage on the sides of my eyes with a wrap around glasses I always have grit in the sides of my eyes. When I do cover the sides I am more comfortable. That may be just me however.