One of my early consulting prospects was someone who basically wanted me to do that for their app, at a similar price point. As I recall, the project went nowhere after they didn't follow up about signing a contract and I didn't follow up about following up.
In hindsight, after learning more about consulting, I am so glad I dodged that bullet.
You are setting yourself up for catastrophic failure in every way with this offering. You will not receive a complete spec from your clients. There are people capable of writing complete specs. They have done successful software development before. They will run screaming from your offering, because they're looking at $1k and 3 days and concluding "He's either insane, inexperienced, or out to swindle us." I plead a combination of insanity and inexperience for saying "Yes, that sounds reasonable for $2,000" to my prospect.
If you get takers, they will be the napkin crowd. The napkin crowd believe they have specs. They do not have specs; they have napkins. You can turn a napkin into a prototype; you cannot turn a napkin into a prototype in 3 days if it is not your napkin, because you will chew far more than 3 days of calendar time and $1,000 (or $2,500) in billable time just doing requirements analysis.
There are also jobs which, if one is not acquainted with reality as experienced by engineers, one might think are doable in three days.
Would you really love to receive this email? "Here's a screenshot. Make it work. I'll pay you a thousand bucks."
http://images1.bingocardcreator.com/blog-images/hn/this-is-n...
Edit to elaborate:
If you're a good Rails/Django programmer, you are at least 20% of the way to a successful consulting business. The market is signaling in a very strong way that it needs them right now. (Ditto mobile anything.) That last 80% is very important, though. It includes things like getting good at estimation and prospecting. I ended up charging off about two months of calendar time to goodwill because I was ludicrously optimistic about estimation and how hard project management would turn out to be.
With regards to prospecting: There are plenty of people on HN who make good consulting clients. waves to consulting clients There are also many people on HN who, and I mean this in the nicest possible way, are not good clients at this point in their lives. Good clients have a clear idea of how the process operates. Good clients cut checks for five or six figures, in a timely manner, without complaining. Good clients have reasonable expectations for what $1,000 will buy them at market rates from someone who is actually capable of delivering projects in Rails/Django. (Hint: not much programming.)