Sadly true that there appears to be no economical options for getting LSD's for non-M E46's. I'm annoyed to no end not to have one. I like my 330 well enough and I'm personally not interested in burnouts but driving on or near the limit with an open diff just isn't very rewarding. I should have researched more before I bought the car. I wrongly assumed swapping in different diffs would be as easy as it is on my E30. Not so. Not by a mile. I'm just learning really about my E46 but i can tell you TMS (turner motorsports) and diffsonline are popular sources but expect to be in for 2-3K in a hurry. As previously stated, using the entire rear end from an E46 M3 is another option but you will have to live with gearing that is probably ill-suited to your car or spend more money to change it's gearing. Someone on the forum is working on making an E30 diff work but it appears that is going to require lots of work.