Can I retire? LOL
At approximately 40 stamps per row, here's over 1400 copies of Scott 720.
In reality, they are hardly worth the postage to mail them to any buyer - or one might argue the 3 stock pages are worth more than the stamps they contain.

(Might there be some interesting plate varieties for the specialist? Possibly, but that's not my cup of tea.)
Gezadrummer, Common sense must prevail when using Ebay data for either the offering price or the sold amounts. Cherry-picking a outlier few listings does not create a true picture of value. There are reasons why a common-looking stamp can go big money ( a truly legitimate rare variety or various shenanigans). Similarly, why a rare stamp can go quite cheap. This comes from experience. Notice also that a lot of 128 used copies sold for $5 + $3 shipping (which is overpriced, imo.) Or a lot of 280 perfins on #720 with much duplication, sold for 6.99 with free shipping.
For Scott 720, printed in vast quantities (a billion or more, I suspect), it takes an extremely special copy (mint or used) to be worth anything. Run-of-the-mill copies such as yours and my 1400+ copies are a glut on the market.
Reminded me of this cartoon:
