How to apply work flow if i have two different plan

hi bubbler.
i have two different plans of payment 50 and 100 if someone select one of them i goes to another step i have 5 steps now i want how should i apply workflow if user select 50 so it charge 50 if user select 100 then charge that user 100.
if i do this through state it is not right method because when someone refresh the page at any step it will erase the state. so please suggest what should i do

Use the dB