My free opinion
When I first started building I went throught the regular research. Decided an egg, then a used Lyco...ended up with new engine.
I am glad I took my time and did what I did and didnt rush into a deal. You are likely aware that there are certified and non certified (big price diff). A quick look at the cubcrafter used engines and I am pretty sure you can do better and get brand new.
Take your time and hopefully a good deal will come along. Osh usually has specials from the builders that will likely save you a K or two off the reg prices plus free ship etc, should be there monday am if you know what you want as they often have limited promos.
Several builders that have great build sites on the net bought used and ended up regretting it due to unforeseen big nasty bills, stuff that doesnt fit etc. If you can swing it, a new engine would be a great long term investment. (Unless all your heads get recalled haha)