Got to ask, what's wrong with the engine that prompted you to say you need a 'rebuildible' engine for it? Unless you've got a block with a hole in it, there's no reason that your engine can't be rebuilt quite easily. Even then there are places that carry cores where a bare block can be bought to start the build.
Barring a rebuild it took me one search for a 'CAT D330 for sale' to come up with an add selling one for $5000. At that price I can tell you for a fact it would be cheaper than a rebuilt. Personally I typically price a rebuilt at somewhere around $2000 to $2500 per cylinder, which includes EVERYTHING from the labor to pull, teardown, rebuild, and reinstall, along with machine shop charges and all parts needed to do the job. In that case it would be somewhere from $8000 to $10,000 for a rebuild, or alot more than a good running $5000 'take out'. Now if you did all of the work yourself, other than the stuff a machine shop needs to do, you might come out for less than $5000 for a complete rebuild, but only if you have the tools and the capability to do it that way.