Hi Wayne,
Welcome to the wonderful world of mystery shopping. I can't comment on that particular assignment or company, but most of the time the fee you see is what you get; there's nothing extra for travel. That is something you need to negotiate with the mystery shopping company.
Everybody starts out by taking lower paying assignments. Don't expect to make big money right away, but also don't be discouraged. Typically the higher paying assignments and bonuses come after you have gained experience and established relationships with these mystery shop companies.
And to answer your last question...yes, always try to get things in writing. Lots of stories on this forum about disappearing bonuses given over the phone.