b) Both are paid apps, the standard version is in-app upgradable to pro
c) We've put a small amount of effort into marketing them via adwords. Approximately $150/month in ad spend results in more than $600 additional profits. Since it is a very niche market, the ads are highly targeted. We're about to branch into some additional marketing on related sites and should be getting some press soon in a big industry mag. Hopefully they will have good returns on them.
d) Combined income from both apps (including in-app upgrades) has exceeded $1000/month for the last 3 months and is growing at a pretty significant rate. This month has already exceeded last month by almost 20%
The apps did require a pretty significant amount of development (client and server apps as well as the marketing website) and my return thus far comes out to about $15/hour but is rapidly increasing.
We're about to begin development on versions of the app for Windows and Android so that we can extend our potential client base beyond just iDevice owners.