Nickel tour: (USA) If someone gives you a nickel tour, they show you around a place. ('Fifty-cent tour' is also used.)
As suggested also in the following extract it refers to an informal, cheap tour usually at a low price, from which “nickel” as a metaphor of the cheap metal low value coins are often made of.
The ‘nickel tour’ is the quick tour given by a person who has expert knowledge of what is being shown. The use of the word ‘nickel’ by the person giving the tour implies that it is being given by an amateur (e.g. the owner of a house, a business, . . .) and that it is not a real organized, planned, or professional-type of tour, but kind of improvised at the moment for the benefit of this visitor (not to say that other visitors might not received a similar “nickel tour’).
And the lowly ‘nickel’ is just used tongue-in-check to emphasize the fact that the tour is kind of ad hoc and casual and that it isn’t really worth the price of (and thus shouldn’t be equated to) a ‘real’ tour.
According to Google Books the expression appears to be from the mid-60s.