Is purchasing goods from a foreign company and paying by transferring the amount to its account in an interest-based bank or by a bank check that is cashed in an interest-based bank considered aiding usury? And is it permissible to purchase from someone who uses the price for something forbidden, such as usury?

"Do not befriend except a believer, and let none eat your food except one who is pious." It is better for a Muslim to deal and trade with those who do not engage in unlawful (haram) activities, so as not to assist them in their sins. However, if you do deal with them, there is no sin upon you as long as you do not participate with them in the forbidden. The Prophet, peace and blessings be upon him, dealt with the Jews despite their engagement in usury. You should hand them the money or check directly, without depositing it in an interest-based (usurious) bank.