From our experience, actual professional floor coating installers do not want to install someone else's product. They want to install their own product for a variety of reasons. One of those is that they are familiar with that product and its idiosyncrasies and don't want to be responsible for a product they are not familiar with. In addition, the small profit they make on the materials is part of the overall profit for the job.
That leaves professional painters and handymen who say it's "no problem" for them to apply a supplied coating. The problem is that they almost always assume that applying a coating to concrete is just like painting a house, wall, etc. It's not. We get more emails from people asking how to solve a problem that was created by someone they hired to apply a coating product that they purchased separately. The biggest mistake these painters make (among many) is that they do not take into account how important it is to prep the concrete properly beforehand. Of course, this doesn't happen every time, but I'm still amazed by the amount of emails we get from people who went this route. Just be careful about who you hire and make sure they know what they are doing.
Just as an FYI, we have found that the first time DIY installer actually takes the time to learn how the coating should be applied properly. They also take more pride in their workmanship. As a result, they end up getting better results in most cases than hiring someone to do it.
In terms of a coating, you have many choices. Our first recommendation would a single clear coat or color coat of a single-part polyurea. These coatings are harder to mess up during the application process, they are very durable, and a single coat would help to keep costs down. We discuss this type of coating in the article below. Each of the vendors we recommend in the article also participate here on the GJ.
Discover the secret of polyurea garage floor coating kits. See why they are easiest to apply, have the best protection and last 4x as long as standard epoxy.
allgaragefloors.com
If that puts you out of your price range, there are other options. For example, if the floor is fairly smooth you could apply a clear modified acrylic polyurethane. These are priced right, easy to apply, and very durable. TS210 is an example. CoverShield U140 is another.
Why TS210 may be the best no etching required, clear coating and sealer for bare concrete, workshops, and garage floors. We test for durability, oil stain resistance, and ease of application.
allgaragefloors.com