The problem with your rent domain is that rent is far different from mortgage. From someone who is heavily invested in the real estate industry, I can tell you that there is no company looking to hit customers on the internet with that kind of domain name. Rent is usually done by independant landlords, the houses advertised through well-established means, and by people who do not have the need to get traffic through such a venture because of the proven ability of other mediums to generate connections.
Also, renters with bad credit are NOT something that is taken advantage of in the renting industry, rather looked very badly upon.
A mortgage is a couple hundred thousand dollars usually, worth persuing if somoene with bad credit reignites their past habits. Virtually no landlord is going to waste their time going to small claims court to get the few hundreds owed by a tenant with similar tendancies.
I think low $$ for MobileDevice.us as its sort of awkward to type in and way too general in a field that is saturated already, but could work well as a redirect page to a company's main site.
Reg fee for the rent one.