If you choose Noxudol, ask them without a leading question about which product lines they are using, pre and post treatment.
A couple shops I spoke to had attractive pricing but only use 900 series, while other shops with a repeatable rate mentioned 300/700 combo. Another shop mentioned they keep it overnight, others said apply in the morning and drive away at night pending no inclement weather. Lastly, another shop asked condition now, explained if its rusty cant be applied over it and must be removed, their hourly rust removal and rust converter pricing etc.
Lot of variation in this product cost.
If you have a good mechanic or a good DIY setup, I'd honestly stick with cosmoline.
It can be applied over surface or light rust, but it must be cleaned first (all loose debris off). The 300/700 has active chemicals that combat existing corrosion and inhibit future growth. The 900 doesn’t do that as it is bitumen based.