Could my dog be pregnate?

my dog went in heat on jan 4th and has been showing in diff ways like her and are getting bigger but no male dog has got in her but my friend has a really horny dog and hops on her alot an everytime he pumps (i guess) he squirts *** every single time is there a possibility that he could have maybe got ger good enough???? she has had that green slime also like her mucis (spelled wrong i know) plug or whatever... Is there anyway that i could tell if she is prego other then a vet because my local vet is telling me its going to be $250 for the vet check and everything and i think thats crazy talk.