Kacper...seriously...you need a different idea. Not practical at all. In 5 years of cruising we didn't see 1 ....Estimates are that 4-6 thousand containers are lost each year. Unless they have flotation (like the recent Doritos containers that ended up in NC's outer banks!)...they sink.
If it were indeed profitable to salvage these containers while still afloat, the shipping companies would do it so since they KNOW where and when they lost a container. If you have to search the oceans for one...it is kind of impossible.