You should be able to find lightly used BMW 3-series for this price point. The Audi A4 and Lexus IS-F that you mentioned would also be solid options. If you can find a certified pre-owned version of one of these, it will help your piece of mind, given the potential cost of maintenance. Infiniti sedans in this price point should also be considered.
If you don't care about brand and like the S3, you should consider a lightly used VW Golf R. It has the same terrific drivetrain as the S3 and is less expensive. You can find them with very low miles for around $30k. Interior quality and features is on par with the luxury brands. Look for one 2004 and newer for the new body style and excellent MQB platform.