The baby web site is very clear , Once you have selected a flight it shows the cost of the flight + taxes and a total
Offers you insurance which you can decline
Asks how many bags or sports equipment you wish to check in and the cost of them before adding to booking
Ask if you wish to check in at airport or on line showing the costs again before adding to booking
The next screen displays a seat map if you ignore choosing a seat and continue it costs nothing
Its easy to pay only the advertised fare + credit/debit card surcharge.