I am working to lighten up another bass headstock--my 4th now. In the process, I have have looked for tuners that are good, light and cost-effective. Full sized tuners seem to range from around 90-115g for reference.

I have not identified any that are good, light and cheap. There may be some out there, but I haven't found them. The cheapest light tuners that I have found may be an Allparts tuner,

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I have found these for around US$16 each. You can get the bass side tuners for that price in lollypop or clover, but I have only found the treble side ones in clover. Right now treble side are hard to find, and I could not find any sets--only a la carte. I have never seen these in person, and I am not sure about quality or weight. I have seen 48g published, which would make them one of the lightest out there...and I am not sure I believe it. Caveat emptor if you buy them...and please let me know if they are any good!

I just picked up another set of Hipshot ultralite "import" (Korean) tuners. There are some small differences between the imports and the USA made, but the quality seems quite similar, as do the weights. The most important difference (to me anyway) seems be that the imports are not reversible, and there are a few options in the USA line that are not available in the import line. Imports range from 50g-57g. USA range from 42g-55g. Variation based on post diameter and tuning key. I have used both. They match their published specs well. I think the imports are the most cost effective on the market. I have gotten them for between US$60-US$72. The USAs are pricier, but still not bad if you can get them on sale... I found my last set for ~US$80. All are available in 1/2" or 3/8".

Gotoh probably makes the lightest tuner, as well as one of the heavier "light" tuners.
GB640 ˝ only (drop in fender) 61.8 g
GB350 ⅜ only (small sealed) 40g
GB750 ⅜ only (like GB350 but not res-o-lite) 60.2g*
GB528 ⅜ only (half size) 59g

* Not technically a "light" tuner, but small and put here for comparison.

I have only used the GB640's. These are relatively big, but if you are replacing standard "big" tuners they will cover the holes. They also have a 28:1 ratio. One a new bass, I might use something smaller, but I really like these. Very easy and precise.

I haven't used any of the other Gotohs. I have always been able to find Hipshots cheaper and lighter...except for the GB350s, that are lighter, but not cheaper. I have stayed away from these so far, partly because they don't make a tuner for 1/2" holes and because the have plastic keys.

Schaller makes some light tuners. I have a set of Schaller BM series on my G&L that has aluminum posts. No idea what they weigh, but the standard BM's are not light at just under 90g. Not sure what the savings is with alu posts, but I can't find them in the aftermarket anyway.

The M90s and M180s are small footprint and are quite light at around 52g. Their BM light comes in around 63g. Hard to find a good deal on these, but they should be high quality if they are like the ones on my G&L.

Grover also makes a lightweight tuning key, the model 143 that weighs in at around 58g. I haven't seen these IRL, but they have a black housing. Not sure if it's plastic or metal. Neither cheaper nor lighter than the Hipshots, so I haven't tried them.

Hope this is useful to someone, and will be interested to hear the experiences of others!