unfortunately both the lab map and the strange potion are very expensive; the only way I could think of that wouldn't cost you would be to ask someone who already has the lab scientist as a challenger if you could transfer your pet to them, have them use your pet in the Battledome to get the gender change, and then transfer your pet back to you. I think new accounts can't transfer pets right away though?
I would offer that for ya but I don't have all of the lab map pieces yet aha