There are some national or regional brands that sell at premium prices, but many small trailers are unbranded or local brands, locally manufactured and sold direct; the big trailer dealer is also manufacturer.
In rural areas, you will find trailers at hardware stores, big box stores like Lowes and Home Depot, farm supply stores like Tractor Supply and Atwoods (or whichever chain is operating in your region).
In urban areas, trailer sales locations aren't so obvious, but it is a category in the Yellow Pages. To haul a motorcycle, a motorcycle dealer can get you one made for that purpose, with bike racks and tie-downs built in, and motorcycle ramps. That tends to be more expensive than the cheapest utility trailers.
Also, be aware that a manufacturer may build, a dealer may sell, utility trailers in different construction grades, with different carrying capacities, so a lower price does not always mean a good deal.
I would look first at a manufacturing dealer, before checking out national brands. Here, that might be Trailers Plus in Tulsa. Where my sisters live in Michigan, it might be US27 trailers on the north side of Lansing. Metro Detroit area, I don't know, haven't been around there much lately, haven't spotted any big trailer dealers, or even farm supply stores, in the nearby suburbs.