I've seen reviews that the people who are selling the refurb often don't check the product and you'll get things like two left hands, two right hands, busted looking headsets etc. I'd say be careful if you do that, I almost considered it but imo, spend the extra 40 or so bucks and get new.

The Lenovo one which has a higher FOV is 200, and it's what i got recently and enjoy it

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