I am putting an E36 M42 in to my E21 (3 series generation before the E30). I have a topic discussing this just below your own. I typically abstain from commenting on a topic I dont know about but since youre in a hurry, I just want to share my experience for your own use before you buy.
Take my words for what they are-- a car that is not specific to your own but let me exercise some caution before you jump in head first.
First off, Id consider throwing in the e36 M42 head and everything that will fit.
I have 3 M42 engines in my garage and 3/3 have bad timing components. 1 guide rail completely shredded and caused the engine to blow. 3/3 had a slightly warped head, 2/3 had a cracked head. If you decide to use the e36 M42, check this before you throw it in your own at a machine shop. Since this thing isnt verified running, have it checked for warping and cracks. Be prepared to replace timing components
The e36 and E30 heads have the same casting number and you should have no issue throwing it on.
The E36 oil sump pan is significantly bigger than the E30. I have to use an E30 sump pan to fit in my E21 and you may run in to similar clearance issues. The e30 pan fits right on the E36 block.
The E36 M42 has knock sensors thus the wiring is going to be a bit different, even if its OBD1.
The E36 M42 Mounting arms are different from the E30 and you may need to re-use these from your block.
$250 isnt bad at all, just make sure you check the timing case and have a pro inspect the head before you drop it on. Get everything he will give you for $250. M42 are everywhere and they dont sell THAT fast. Unless this is your DD or something, you dont have to be in a big rush and its not a terrible idea getting a GOOD M42 shipped to you (I wish I considered that when I was buying, I ended up spending more in the outcome)