Welcome! Lots of great help if needed. Your location is missing.
As for Sling N Steel custom smokers never heard of them. They advertise on Cra*igs Li*st and have a Face*book local business listing in the Whitesville, Kentucky area.
They are similar to most small independent builders here in Houston.
An entry level, reverse flow, trailer, model appears to be $1,650 (USD). My Klose 20" by 36" backyard smoker was more than that 2 years ago.
Supposedly 1/4" steel.
They do apparently support charities and church efforts.
Looks like a couple of guys trying to make a living. Be careful, ask lots of questions, figure out what you need, and be "eagle eyed".
Best of luck!