If I'm not mistaken, ESEE pricing does not include a sheath
Yup, you are mistaken. They can come in any configuration you want. No handle scales, no sheath, only with a sheath, with sheath and molle back. By far the most common configuration is with either kydex or molded plastic sheath which are all very good IMO.
Here is my take on the BM Nim. I have had two. One was the drop point (never had the tanto) with serrations and the aluminum handle. Great looking knife and would no doubt be very good at taking out sentry guards. It just was not as good at being a daily use all around knife. The second one was plain edged and had the older G10 handle. The handle was much more comfortable but again, I had other knives that just worked better for my uses. Also the sheathes were not great. The nylon one is not bad but really needs to stay strapped on a pack or vest or something. Forget about moving it from platform to platform quickly (IE taking it on and off your belt). The kydex was just plain old funky. Great design idea that was poorly executed.
I would also second an Esee. They are a great value (at least here in the states). Great Fit/finish, great heat treat on the 1095, great sheaths, and one of the best warranties in the buisness (forever, transferable, and no questions asked). There is even a story where a guy down under broke his Esee 3 and Jeff sent him a new one with only seeing pictures IIRC.
The Ontario RAK you mention being cheaper is so for various reasons. For all the reasons I mention Esee is great the Ontario will be less great at. IMO, particularly the sheath. A terrible sheath can make a great knife not worth carrying, again, IMO.
If you do consider an Esee (or any other knife really) you should also consider what you will be doing with it. If you are planning to cut out from the fuselage of a helicopter, the 5 would be great. It is not that great at being a knife. .25" is impressive but not very good at cutting stuff. I have one and it is awesome but it really is more of novelty. I have had the 4 but found it to still be thick for it's length. It is just as thick as the 6 but the 6 justifies it better with its length. For me the 3, 6, and Junglas are the best Esee makes. The 6 is a great jack of all trades but master of none.
If you don't want to swing the price for the Esee take a look at becker. They have a knife in just about every length or thickness. They are cheaper but their blade steel and heat treat is on par or better than Esee (they use 1095-crovan). Again though, they are cheaper because many of the nylon sheaths aren't very good and they don't have micarta handles. But lots of people love them!
And just a word on 1095 (or the cro-van). I wouldn't worry much about maintenance. They are coated so the only part of the blade to worry about is the edge and most any use it sees or sharpening gets rid of the surface rust. Just lube it and you should be good. Also it is easier to sharpen than stainless. Esee recommends the sharpmaker which you already have!
A final thought, have you thought of more local stuff like svord? they make some good budget stuff that you could get you feet wet with to find out what you like.
And a pic:
