Why is gusta singular
 

http://www.palms.com/wp-content/them...=328&zc=1&de=0

tacos and margaritas is plural. Why isn't it gustan?

1. The ad is bilingual; the only thing in Spanish is the phrase "me gusta".
2. In this context, one can think of the situation (having inexpensive food and drink) as the subject, and the situation is naturally singular.

Exactly!

Tacos and margaritas, just 99 cents? I like that / I like that woman (Me gusta [eso/esa])

That's probably how the add is brain read.

"Me gusta" is no intended to "tacos and margaritas" but to get each of them at such a price.