got it.

Thanks for that.

To deal with the sentence successfully you first need to consider its meaning. The sentence lists five items, four of which support the claim that cats' needs are "simple and largely inexpensive." You know that the fifth item, the trips to the vet, aren't part of this list and shouldn't be parallel with it because, first, the and before shelter suggests that the initial list ends with shelter and, second, trips to the vet are not inexpensive. Therefore, the final item needs to be expressed as an exception. Eliminate (1). At this point, the primary problem is one of expression. Veterinarian visits, while shorter, is less clear and idiomatic than visits to the veterinarian. Out with (2). As for (4), we have a dangling modifier: who is occasionally visiting the vet? Eliminate. Finally, (5) is a passive and much wordier option than (3). (3) it is.