Thanks for looking
since you have a tele already, the cheapest and easiest would be to use a diopter on the 18-200, Raynox are good ones but I've heard of vignetting problems in that particular nikon lens
Another option would be to get some tubes on the 50mm, and maybe a diopter on it as well, you would easily get more than 2:1 but wouldnt be exactly cheap since tubes with contacts go for around U$150 and the diopter U$60
I have a 50mm and played a bit with the combination I said above, it works but I used it mostly for curiosity since my fave setup at the time was the 70-300 with a +8 diopter.
My close-up is a DCR250, the bee was only with it and the 50mm, and the two others had also 20mm or 32mm of tubes
But still the cheapest would be reversing lens, any old wide U$15 lens would work
Reversing modern lens is no good because you lose aperture control, with the old ones you just dial it on the lens barrel itself. If you wanna reverse one of yours (the 50mm would be the best) just out of curiosity, the reversing rings go cheap on ebay, like around U$4 I think