Bugtracker with certain spec. needed

Searching a bugtracker which fullfills the following specifications. It can of course be existing software, but shall be free or cheap. If the system is rather complicated to install you might also offer a price for initial installation and configuration. Set up admin, 2 sample projects and 2 programmers. Specifications: general: - user groups: clients, programmers, admin - projects - user defined bug-status - priorities - configurable email-alerts - no installation of own services (shall run in normal hosting environment) specific: - Client can login and see only self reported bugs or bugs which are enabled to see for him - specification if a certain comment/update on the bug shall be visible to client or not - Client shall not see which specific programmer is working on his bugs (programmers are externally shown as company-name) - internal surface shall use colors etc. to indicate bug status - programmers shall be able to hide certain projects in their view - admin shall be able to enable projects to certains programmers - programmers shall be able to specify certain bug status as to be hidden by default (e.g. do not show completed or unclear bugs) We've been using bugdar till now but it does fulfill far not all requirements.