If you really need to run on a Linux server, your options are a bit limited, but not impossible. SugarCRM and
EnterpriseWizard are both reasonable options and will come in at your price point. Pros and Cons: SugarCRM has robust SFA functionality, but scalability is suspect and I have heard that it is a nightmare to configure and maintain. Of course, they may solve the scalability problems before you really need 1,000 staff logins.
EnterpriseWizard is more focussed on Support Automation and is weak on SFA, but they have a great reputation for scalability/deployment time and claim to be beefing up the SFA functionality.