I still don't know what kind of substrate you have or if you need to install a backer board or what? You can't just install the tiles.
Thinset mortar costs from under $10 for a 50 lb. bag for unmodified, to from $14 or so and up for modified mortar. The type you buy depends on the subfloor and the specific kind of tiles being installed. If the subfloor is wood, you will probably need to do some else first?
Grout usually cost $10-20 retail, unless you buy epoxy grout, which a novice should avoid.
The pre-mixed stuff is nothing more than an acrylic or mastic product. When used in damp areas it'll re-imulsify to its original state and fail. Most mastics should not be used around damp areas and are not a good choice for floors....even dry floors.
For this you will pay 5-8 times more. A 50 lb. bag of thinset does 80-100 ft. of area depending on the trowel necessary. This $10-15 bag is equal to about 5 gallons of mortar. You do the math.
I'd be interested in knowing what kind or thinset costs $48 per 50 lb., and what grout is $34.50? I'd also like to know who sold it to you.