Im gonna have to say DIY.
Now, I haven't ever really payed that much attention to the oil pan, so it may be a serious bitch to remove from an e36, but dropping the pan itself isnt that hard to do. It's just like changing the oil, only you take a few more bolts. Swap the gasket, and put back in place. Given that its a $500 operation though, I would have to assume its one hell of an expensive part or either motor has to be pulled or suspension components removed to allow the pan to be removed.
<span style='color:gray'><span style='font-family:Courier'>1995 e36 3 Series RIP
1999 e46 3 Series BURN IN HELL
2000 MR-S Roadster= Current</span></span>