[husker boxster]

The further you get away from Porsche components, the more expensive the proposition becomes. While 911 engines aren't exactly plug and play, they're close enough that the expense of the engine is worth the 100 extra hp. An Audi V8 works because it will bolt to the Porsche transaxle but you have to figure out motor mounts. An LS1 swap may work because they'll have the trans part figured out, but you may have less room in a Boxster than a 911 for the swap, so that complicates things. Once you get away from those options, everything else is an engineering exercise. You have transaxle, motor mounts, and computer issues to work out. If you're planning to have someone do the work for you, you'll need a big, open-ended budget. No way someone can estimate the cost because they don't know what they don't know. Costs will quickly escalate as they run into problem after problem. Some will just take extra time (which = more $$$) while some will require special machining (costing $$$ for the part + time for the extra labor). If you were doing the work yourself, you could get by by not counting your labor.

If you want to experience the joy of owning a Boxster, find a nicely cared for, running example for $7-9K and sell your Nissan engine. Your wallet will be miles ahead.