This eye-opening, informative flier is originally from the Companion Parrot Connection (CPC) and was published in 2005-2006. It gives you an idea of how much it costs to care for a companion parrot.
Budgies and Cockatiels can get along but it depends on the individual bird. After proper quarantine, you can start with putting them in separate cages side by side so that they can get used to each other.