Well lets take these in order.
Depends on how you are storing your data. You could put it in a database
and use the text search functionality that goes with your database. Or
could store the information in a NoSQL document store, so you will need
gem that works with the document store to do the search. Or you could
the data in text files and write your own search engine (not as crazy as
sounds). Or you could use an XML database such as eXist or Marklogic.
could split your data between a database and some other form of storage.
Without knowing your data or your requirements or the technology you
to use this is the best answer you will get.
-> Bidding functionality.
You really need a gem for this? Write your own
-> Login / Registration
Devise is a comprehensive solution
What do you mean ‘messages’. Tweets? Emails? Popups? Forums?
-> Financial transactions
What does this mean? Are you going to invoice people? Are you expecting
make one off changes to someones credit card? Are you intending to make
recurring charges to someones credit card? Will you accept Bitcoin? Will
you accept Paypal?
With nothing more than vague bullet points you will get nothing more
overly broad handwaving.
What do you mean Admin? Admin for users/login? Admin for bidding? Admin
There are quite a few of these ‘job / worker’ auction sites. Why not see
you can licence their codebase. Seriously.