I can also second the Malkoff drop-in. I guess it could be considered expensive (because it is), however, it may be truly the best bang for the buck because of the absolute perfect engineering and construction.
I have built many a LED light and really cannot get any of my lights to equal what Gene has done with his. I believe his electronics are of very high quality and allow the single LED to be the brightest it can be. I believe he has his electronics custom made for him.....and only him.
There are lower cost options, but do a search and you will find that really there is nobody out there who has a complaint about Gene's drop-ins. Seriously, they are very good.
Bob E.