Anything you swap in is going to be expensive. Scott Riley from Sport Rider in WI just put a 2JZ engine out of a Toyota Supra in his. Last time he was on the dyno he was around the 400whp mark. You can find those engines fairly cheap and from what he was telling me in Maggie the majority of the parts to make it work in the SS were fairly inexpensive. But it will all depend on the condition of the engine and how much of the work you do yourself. If I had to take an educated guess Scott probably has around $10k just into the 2JZ engine setup. It really all comes down to what your definition of expensive is, what your goals are, and what your approximate budget is. It's really easy to dump $8k-$10 into a fully built engine and turbo setup on one of the LE5 engines that come in the Slingshot.
We also make a forged engine here at ZZP. You can see it here https://zzperformance.com/coll…3-forged-2-4l-short-block We offer it as just a short block but we can build it up into a long block for you as well. There are a lot of options in building it up so it's always best to talk to the person and look at budget and power goals so you can make sure they get everything they want/need to reach their goals but not sell them anything they don't need to get there. I have sold 10 short blocks and built another 5 of them into long blocks over the last 4 months and everyone has been very happy with them. Three of the short blocks and all 5 of the long blocks were installed here at ZZP and all of them were running our turbo kit. They all left making between 9-15psi of boost which is between 300-400whp. If you still are on 3 wheels, 400whp is way more than you'll ever need. We had a short block and ported head go to TX to a guy running a supercharger and he has also been extremely happy. The point being we can build to suit anyone's needs running any companies parts. We will also have a drop in turbo engine swap option next year that base power will start at 250whp. Stock internals will handle 400whp and the block will handle 500whp. There will be 3 turbo options available depending on what your power goals are. If you are interested in discussing any of this further, you can always email me directly at Kyle@zzperformance.com as well.