If I'm still unsure...Ask a property manager, a realtor, other landlords in the area, search rental listings like you were searching for a rental comparable to yours then adjust up/down based on your condition and amenities.

I was definitely having difficulty justifying 50% down to yield something comparable to a savings account.

Revenue growth isn't tied to interest rates, it's tied to supply and demand in the rental market, plus what other comparable properties are charging.  

Look at mobile homes that are that age already and see what they are valued at and compare to their original purchase price.Is this located in a mobile home park?

What are the advantages/disadvantages compare to other types of real estate investing.  

Paying an attorney is still a bargain compared to a problem tenant. 

Tell them to look at local listings which are comparable in terms of rooms.

Compare an extra hundred bucks a month to having to do a $10-15k renovation now, between tenants, and in a year after the new tenant leaves. 

All of these factors will pay off disproportionately over time compared to what it took to get them and is worth the time.

Now before you guys go thinking I haven't looked for this.........I have, but I love to have options on the table especially so I can compare.