Is one allowed to put up a ceiling fan during the Omer (there is not sufficient income to have it done before the Omer)
There is no problem in putting up a celing fan in the omer period.
Sources: Although it is a time of mourning for some matters, such as not having weddings, the time of the omer does not share the stringency of Bein Hametzarim or the Nine Days. Poskim therefore write that it is permitted to buy new clothes, and so on, in the omer period. It is likewise permitted to renovate. See Mishnah Berurah 493:2.