I agree with Don Tepper except that there are some very high end modular homes that started in the high $300's to low $400's in Chapel Hill, now sell for $500k+. Acorn and Deck are those modulars. Otherwise the lower end often look like upgraded manufactured homes, sorry to say.
On the other hand, they can be very affordable and certainly the right option for many people.
The point I'd focus on is: For the same amount of money, what can you buy in a stick-built home versus a modular home? What's the upfront cost? What are the monthly costs? What is the quality of life like?
And if your client is an investor, then look at the purchase price versus the rental income. In many areas, you'll get a much higher return on modular homes than on stick-built homes.
Hope that helps.