Joomla Food/Recipe Website Needs Repair

My food and cooking website is down due to an attack via an insecure script installed on the webspace. According to my web-host, 1 & 1, hackers processed the attack through a security leak in our software, I would like this fixed. 1 & 1 gave an analysis of the attack and possible fixes. That is what I want done. Give me an idea as to cost and time. I communicate primarily via email. Thank you. 1.1 The hackers processed the attack through a security leak in your software - Joomla! They misused at least the following modules or files of this software: ./administrator/[login to view URL] 1.2 Via this security leak the hackers have uploaded the following malicious files to your webspace: ./components/com_agora/img/members/2/[login to view URL] 1.3 In order to impede further attacks, we have disabled these files. Please note that part of your websites may be impaired. ****************************************************************************** 2. Required measures ****************************************************************************** In order to reactivate your websites and re-establish the security of your 1&1 account, observe the following instructions. 2.1 Delete all aforementioned files. Note that hackers usually come back to a webspace they exploited successfully. 2.2 Upload a more secure version of the following modules of your software: joomla 1.5.23 ~/ 2.3 Please urgently change your Administration Password to the indicated software. 2.4 Also check whether the hackers have changed the content of your data base. Please look out for the following: - Are there new users? - Has malicious content been inserted to your data base? 2.5 Check whether other malicious content was uploaded onto your webspace during the attack. Delete all unknown, suspicious files immediately. IMPORTANT: In the future, please check the security of the software you install on a regular basis. We will assist and help you with any specific problem, but please be aware that the security of the software you install is your sole responsibility.