How likely is it that pre-ejaculate will get you pregnant?

Yes it is possible: Pre-ejaculate does have sperm in it and it only takes one sperm to fertilize an egg creating a pregnancy.

Variable: Most studies have shown low levels of sperm or no sperm in pre-ejaculate with sperm not being motile. One small study published in 2011 showed that there are some individuals with a high motile sperm count in pre-ejaculate. See: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3564677/ Pre-ejaculate