Currently, at Groupon, you can get a lifetime product key for Microsoft Office Professional Plus 2019 for PCs for just $14.48 when you use coupon code QUICKDEAL at checkout.
Note that other coupon codes may be available. Promo codes can vary based on user or location. Check the promo box at the bottom of the description to see what code you qualify for.
This lifetime key is regularly $149, but it's on sale for $16.09 (before the code) — that's an 89% total discount. The 2021 version is also discounted to $20.25, also down from the original price of $149.
If you're a Mac user, you'll still get a discount on the 2021 version, now just $96.39 with the code — regularly $149.
If you're worried about the authenticity of the product, you can rest assured that the seller is a certified Microsoft partner.
Make sure to stay on top of the best deals by getting in touch with KCL.