They all have their purpose and limitations.
1. Dowels are good for end grain to long grain joints of small components where size limits or other factors dictate ( aesthetics for instance ) Vs a M&T joint. One could also throw pocket screws in the mix here as well, this is what I typically use, but my application is generally a smaller face frame cabinet joint. Depending on how many are used and the size, dowel(s) could be used for light structural use.
2. Biscuits in my experience are good for edge gluing as an alignment aid and nothing more. I wouldnt personally count on one for any sort of structural application.
3. Dominos, like dowels, are very strong but do 2 things dowels cant, one, you can use one domino in lieu of 2 dowels (faster) . secondly, one domino can align a joint in 2 directions, sliding and rotation of the joint . This ensures faces stay flush and planar when gluing (quality) . The domino tool expands on the dominos capabilities as far as applications with its (extreme accuracy) and (flexibility) allowing you to use a domino where a dowel might be difficult to installed repeatedly or accurately. Dominos are available in many sizes , length and widths and can be used from light duty to structural applications like doors.
So, to answer the budget question (targeting the domino mainly) , what do you need to make and can a joint be made alternatively?. Do you need speed, quality and flexibility foremost (think professional)?