What the article does not seem to mention is that an usual electric wheelchair costs about $65,000 (and is intended to be replaced every six years or so). This and the non-availability of replacement parts is why some wheelchair users started a project to open-source a wheelchair from standard parts: https://themif.org/ Louis Rossmann interviewed the founder of the project here: https://www.youtube.com/watch?v=eaAj59…
Should be "a usual" because "usual" starts with a consonant sound. Otherwise could sound like "unusual."
"Electric wheelchairs usually cost a lot of money."
vs.
"A usual electric wheelchair costs a lot of money."
The second form begs the question, what is it that comprises a "usual" electric wheelchair? What would make an electric wheelchair seem "unusual"? A custom muffler? The statement creates more questions than it provides answers.
The first form however is simple and clear. What about these wheelchairs can be considered "usual"? The cost. They cost about the same. What would make a wheelchair expressed in this context unusual? The cost. It's either cheaper or more expensive. No additional unanswered questions have been created by expressing the statement in this form.