I have just checked coupons. The lowest price I could get is 15.99 USD for 90 Degree (in Banggood). Get coupons, create price alert or check price history out! You probably want to know what is the best price?
Latest coupon and price update (UTC):
Banggood (15.99 USD)
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. Well, is it a good price anyway? Maybe there’re no more promotions for this item, because current price is higher than average (which is equal 11.99 USD)
Link: Banggood product page
Price: 15.99 USD
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): BGherra, BGBFCR32, BGsqus18, BGsqus20, BGbackwo, BG18baofu, BGDRB18, BG17331, BGb77dcc, BGWT15, BGa0b557, BGc8412f, BGWDT15
(these coupons are old, so probably won’t work)
Aliexpress
Click here… to search for 100x70mm 90 Degree Angle Corner Square Ruler on Aliexpress
Here are coupons that you can use.
Price history and price alert
Price history (for all/most countries) for 100x70mm 90 Degree Angle Corner Square Ruler is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).