I did it myself in my previous dining room. It takes a lot of planning and precision, a level, caulking gun, miter box, nail set. My DR already had a chair rail. If you don't have one, the project is still do-able but probably a little more effort depending on the corners. I think mine looked professional. It is a matter of being neat and level and making clean cuts and sensical placement and sizes. Mine was not thick moulding. I was keeping it scaled small intentionally, but it would not have made any difference. My miter saw can handle much bigger wood than that.

At roughly $50/hr (depending on your market), perhaps they are speculating a 10-hr job. That may or may not include time to acquire the materials. How big is the space? Does 10 hours make sense to you? Sounds about right for my pace and my 10x13 DR.. A pro should be faster. It also takes time to plan the frames sizes and just where the frames should go to be even and perhaps go around obstacles. I worked and reworked some of my placement issues for quite a time before I finally cut a piece of wood. Started on paper. It's not rocket science. You may want to be involved in that planning even if you go pro.

As far as matching what you have, you can take a few pictures and measurements of your existing and go to a lumber store to make sure you can get the same material. I would bring home a sample to be sure before buying all of it. And always get 10% more than you think you need, maybe 20% more to be safe as a newbie.

Those little pieces of wood on the left are my spacers to make sure each box is evenly spaced from the previous.

I just re-read your post. 5 frames is not much. the quote seems high.

That sounds extremely high to me. I'd DIY it as it's very easy to do so. All you need is a tape measure, a calculator, the wood, a miter box and saw, finish nails and hammer, and paint.

Thanks to all! You've convinced me! I am a detail person. I can do this!!!! Wendyb, I appreciate the information, very helpful!

I have done this in a few rooms. At the time, I used a simple miter box (didn't own the miter saw yet). You will be surprised at how inexpensive it is too. Start by drawing pencil lines on the wall where you plan for the squares to be placed. It's like a jigsaw puzzle. Good luck. show us pictures when you are done. My only suggestion would be to prime and 1 coat of paint before you apply molding. t saves some painting time at the end.

I remember one of the more challenging parts was deciding the amount of space between, above and below boxes. There are a gazillion options, especially if obstacles like bulky baseboard heaters and low windows.

In your case, because you are following existing frames, that will be much easier. If you have to make a small frame because of where a wall ends, that's fine. One small frame is preferable to adjusting the size of all of them to be different than the existing ones just to fit on a wall evenly.