Try Amazon US, there are some certified refurbished HP ones available for $150 now:

https://www.amazon.com/HP-Reality-Controllers-Certified-Refurbished/dp/B07CSFYJKD/

new ones are $250:

https://www.amazon.com/HP-Mixed-Reality-Headset-Controllers/dp/B077MF8TQ7/

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Lenovos were going for 109 a couple of weeks back but sold out very quick. Right before that Dells were going for 150 on sale. Amazon has Lenovos for 199 right now and refurbed HP's for 169. Finding one for 100 will be lucky as that was a very limited promotion. Realistically if you want one today, you will find one for right under 200 to 250 which is still considerably less than a Touch or vive.

Best price I can find right now is the HP for 169 from Amazon. Refurbished from Amazon you have 90 days to return if you have any issues. All the WMR headsets are all pretty comparable to each other very minor differences. I have the Acer which is supposed to be the worst of the bunch but I absolutely love it.

HP WMR 169@ Amazon -refurb

https://www.amazon.com/HP-Reality-Controllers-Certified-Refurbished/dp/B07CSFYJKD/ref=sr_1_5?dd=DoPIaQGjTJmlMsMv6SFCXQ%2C%2C&ddc_refnmnt=pfod&ie=UTF8&qid=1534630072&sr=8-5&keywords=wmr+headset&refinements=p_97%3A11292772011&dpID=31mE1RzPUWL&preST=_SX300_QL70_&dpSrc=srch

Lenovo WMR 197@ Amazon - new

https://www.amazon.com/Lenovo-Explorer-Wireless-Controllers-G0A20002WW/dp/B0764GKZ15/ref=sr_1_4?ie=UTF8&qid=1534291395&sr=8-4&keywords=windows+mixed+reality+controllers