You can get GM12-N20VA DC 6V 18rpm Worm Gear Motor Gear Box for $18.39 with coupon (from Banggood). Go down and check coupons out. Remember to check price history if it is available. Do you want to know what the best price is?
Latest coupon code price check (UTC time):
Model CHW-GM12-N20VA, Ratio 16: 00, No-load current ≤ 70mA, Stall torque ≥ 4.0kg.cm, No-load speed 18rpm, Rated-load current ≤ 0.25A, Max power 0.6W, Rated torque 3.0kg.cm, Stall current ≤ 0.65A, Rated-load speed 12rpm, Voltage DC 6V
Banggood ($18.39)
Banggood warehouse is located in China. So I have checked for active coupons (all category coupons and old ones), but there was no working coupon in Banggood. But wait a sec… Is it a good price? Maybe there’re no more promotions for this item, because current price is higher than average (which is equal $14.94)
Link: Banggood product page
Price: $18.39
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BGGines, BGTools8, BGMCT01, BGTACC18, BG589b2e, BGHTT15, BG20236Tool
(system checks these coupons on every price check (like once per 24 hours), but you can check them out anyway)
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Price history and price alert
Do you need price history chart (for all/most countries) for GM12-N20VA DC 6V 18rpm Worm Gear Motor Gear Box? There we go.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).