How fussy are you about appearance and how badly cracked? If not too bad and not blatantly visible, I would probably (carefully) get some ABS cement on the mating surfaces of the crack. After it dried, I would put some epoxy over the inside and lay some fibreglass cloth over that. One more coating of epoxy and you are good to go for the life of the bike. A good repair will leave a fine line that won't be noticed unless you are looking for it. Or for $77.19 you can buy a new, painted front fender.
https://www.yamahasportscenter.com/fiche_section_detail.asp (Link goes to aftermarket parts site but not to the actual fiche for the part) For the price of a new fender, it would never be worthwhile to paint the repaired one!