i don't think there will be boycots from fans. i think fans still want to come from various regions, its more that the prices are way too high for everything, or people visas being rejected or expensive, or even being turned away at the airport. that is what will more than likely cause lower attendance. at least for the countries that dont have big fanbases.
i don't know how low will prices go. i dont think the club world cup is a test of it ( although some stub hub prices have been dropping for group stage games)