I faced the same dilemma. My '02 Boxster S had intermix, it turned out to be a bad cylinder crack. My plan was to look on CoPart.com to find a wrecked/burned etc compatible car, pick it up and swap the engine in. The cars on there go VERY cheaply sometimes. The problem with these cars is that although they're wonderful cars, they just aren't worth much. I know everyone has their own opinion, but to me personally, it's financial lunacy to put a $15K+ engine into a $8K car.
You can buy a wrecked or otherwise damaged 986 on Copart.com for less than $4K all day long, I have seen them go for less than $2K on occasion. Pull out the engine, swap it into your car, and then sell the remainder of the car you bought to recover some of what you paid. Of course you can ping Woody on here to see what engines he might have laying around too. There are others on here who sell engines also.
To me, given the very limited value of these cars, a used engine is the only logical way to go. Obviously check the used engine out very carefully before you go through the bother of installation, and it's a no-brainer to do the IMS, RMS, clutch and AOS while it's out. Others obviously have a different opinion. Your mileage may vary. God luck, been there, done that. It sucks.
https://www.copart.com/lotSearchResults/?free=true&query=boxster%20s