It's less convenient to multibox now because Deca actually makes an effort to ban for it and unnamed accounts can't get soulbound loot so you can't avoid bans that way. Most people who multibox now open dungeons with keys and sell "dungeon runs" using other peoples accounts as a service.
As for paying for multibox programs, I don't think anybody does. As far as I know, people either use old cracked versions of Kronkboxer, SPC style multibox, or some private solution they make themselves.