A USB4 peripheral interface is $15 and a 10g ethernet IC is like $80 at least, plus a little box, SFP+ thing, other physical items. Seems hard to get the price down that low and still make a profit. Plus the buyer still needs an expensive cable on both sides.
A 10G PCIe card is only $100 retail so $150 seems fair for an external version. Newer dongles will include a captive USB4 cable. And consumers use base-T not SFP+.