[Question] Why is this utilitarian calculus wrong? Or is it?

Sup­pose that I value a wid­get at $30. Sup­pose that the wid­get costs the wid­get-man­u­fac­turer $20 to pro­duce, but, due to monopoly power on their part, they can charge $100 per wid­get.

The eco­nomic calcu­lus for this prob­lem is as fol­lows. $30 (wid­get val­u­a­tion) - $100 (wid­get price) = -$70 to me; $100 (wid­get price) - $20 (wid­get cost) = $80 to wid­get pro­duc­ers. $80 - $70 = +$10 to­tal value. Or­di­nar­ily, this wouldn’t im­ply that util­i­tar­i­ans are re­quired to spend all their money on wid­gets be­cause for a func­tion to con­vert dol­lars to utils u($), u’($)>0, u″($)<0 and wid­get-pro­duc­ers usu­ally have higher $ then wid­get con­sumers.

But sup­pose the wid­get mo­nop­o­list is a poor worker com­mune. The prof­its go di­rectly to the work­ers who, on av­er­age, have lower $ then I do. It seems like buy­ing wid­gets would be more moral then, say, donat­ing $80 to the same group of poor peo­ple ($80 - $80 = $0) be­cause the wid­get pur­chase slightly com­pen­sates me for the dona­tion in a way that is greater then the cost of the re­cip­i­ent to pro­duce the wid­get.

And yet, I feel even less moral com­punc­tion to buy wid­gets then I do to donate $80 to GiveDirectly. Is this just an ar­bi­trary, un­jus­tifi­able, sub­con­scious de­sire to shove eco­nomic trans­ac­tions into a sep­a­rate do­main from char­i­ta­ble dona­tions or is there ac­tu­ally some mis­take in the util­i­tar­ian logic here? If there isn’t a mis­take in the logic, is this some­thing that the Open Philan­thropy Pro­ject should be look­ing at?

[Ques­tion in­spired by a similar ques­tion at the end of chap­ter 7 of Steven Lands­burg’s The Arm­chair Economist]