The FDA standards say that raw salmon should be frozen at -20C for seven days before it's safe to eat. My freezer goes down to -25C. Salmon in my supermarket is considerably cheaper if it's not frozen. Can I buy that salmon, freeze it at -20/-25 at home and eat it raw without significant risk, or am I missing some other requirements?
If the salmon is cheaper "raw" than frozen, it's probably a product that was frozen and then thawed so subsequently refreezing it will have the opposite effect of what you're trying to accomplish as thawed products must be cooked before being refrozen to ensure bacteria introduced during the thawing process are eliminated.
That being said: we cannot give you good advice without actually holding the salmon and feeling and smelling to ascertain it is not a thawed product. You should ask the supermarket's HQ if refreezing that product would be safe as the local people will probably not know...