Looks like harmless surface rust to me. If the guts are good, the value of it depends on where in the country you are. They seem to sell really cheap in the midwest and northeast, but here in the southwest where I guess more people do SAS's and the demand for axles is higher, that's a $250-300 piece there. That one is good because it's complete knuckle to knuckle and has some core parts, and that steering can be pulled ad used for spare parts as well.

Clean it up and use it!