It's a complex pun referencing the previous line. Saul Goodman has told Walt that he's up shit creek, which is an idiom meaning that everything is really, really bad. He then "jokes" that Walt can "buy a paddle", which is to say that he can buy a way to navigate shit creek. That thing he's buying, in this particular case, does happen to be secret relocation services, aka "vanishing". However, that's not what the phrase HAS to translate as; "buying a paddle" would simply mean buying any particular thing that could help with a particular shit creek.