It would be better to simply use the adverb form "usually" and apply it to the word "cost", instead of using the adjective "usual" and applying it to "electric wheelchair".
"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.
"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.