Good morning,
my name is Christian and I am a professional Ruby on Rails developer since 2007.
The project you are proposing is exactly what I do everyday at work, that's why I am able to offer you exactly what you need for a reasonable price.
Regarding the deploy infrastracture, it depends on how many users you plan your system to have in the first months after it will go online. As you know, each deploy option is different in terms of price, scalability and flexibility. My personal idea is that a custom configured VPS is the best for the early stages of a web projects, because it generally costs less money and it can grow quite easily, while not limiting the flexibility of a more closed solution like heroku. AWS could be a good option, but I don't have much expertise in setting up a full amazon based solution (I often use S3/cloudfront for content delivery, I used some EC2 VPS and the postgres hosted service in the past though).
I also have experience with Mandrill (that is very simple to use, I know) both for sending and receiving emails (in case you need it) and I mangage SSL certificates daily at work.
As I am a full time employee, I can work on freelancer projects in my spare time, so in the evenings and weekends, Italian time.
I know this could be a limitation, that's why I wanted to be completely clear about this point.
Feel free to ask me any question you might have and good luck for your project
Christian