Project Cost Estimation

Hi all,
I’d to ask for your cost estimations on a web app project i am about to
take. Im fairly a newbie on the market, yet my programming skills are
sufficient for this endeavor.
In a nutshell here are the requirements:

the client is an conference organizer-travel agency located in Greece
employing about 10 people.
the user groups for the dynamic part of the site are: abstract
submitters (AS), abstract reviewers (AR), the agency administration
(AA), conference participants (CP) who do not submit abstracts

The desired functionalities are:

  • bilingual ui (greek, english)

  • a cms’sy system to:
    make it able for AS to submit an abstract, the system should then
    automatically notify the Î?Î? to login and evaluate and rate the abstract.

    make it able for CP to register online and pay for their
    participation in the confence (ecommerce-payment integration)

    the AA has to be able to maintain, new conferences, AR’s for each
    conference, statistics, etc

What are your estimations on such a project demands in hour and cost
(given Im gonna do it on my own in Ruby on Rails)?
I asked around and was given from 30 to 50Euro per hour feedback.
What do you think?

many many thanks!