A book’s worth of great stuff has been posted on this topic here and in the other forums, you might want to do a search on them.
There is no set rate for making a commercial. I believe the right way to go about it is to start with a creative treatment and script; using those as a guide to plan the shoot, figure a rate for the shooting, then calculate all true obvious and hidden expenses to arrive at a sensible rate for the edit. Then it’s rate x time spent + profit margin + expenses = fee. You make adjustments to be somewhere in the middle of the range your competition charges, or if you’re good enough and demand is high, you charge whatever the market will bear. I have worked on award-wining 50-dollar spots, and I have seen real junk produced for thousands.
I see a lot of local cable spots like the one you describe, and most of them look horrible because they were done on too low of a budget and they cut corners on good lighting & composition,
(especially deadly on food product shots for local eateries)
really atrocious audio, and derivative, uncreative editing with cheesy graphics and music.
Not to mention the script was inept and not done using a proper process. I’m not saying yours will necessarily make all the same mistakes, but these are things to watch out for. To do it right, it costs what it costs.