I've been doing this type of investment for over two decades. The cost is a fraction of what a comparable size stick built would be. I get rents very close to what a stick built would bring. There are renters that don't care if its a mobile home. They're not buying the home. They want a certain number of bedrooms, baths, and square footage. You have to inspect and maintain the home religiously, but its so worth it. After many years of renting out the property you can sell it and carry the contract. You'll then have many more years of income without any upkeep worries.
As a side note, I made most of the money to build up my rental house portfolio by flipping mobile homes in parks. Most investors scoff at this, but with profit margins of 50% to 200% compared to real estate flip margins let them laugh. There has always been plenty of projects to choose from with very little competition. In parks, the homes are personal property, not real estate. They are bought and sold just like a car or boat. Takes little money, the houses are easy to inspect, simple and inexpensive to fix up, and the park is responsible for all the infrastructure.