I wish people would see budgies for what they are, small parrots
they need a wide cage rather than tall, as said above, and lots of natural climbing/roosting perches, apple branches, from a pesticide free source are great for them, theyll have great fun peeling the bark too, budgies, like all parrots love to climb and, unlike finches and canaries, fly horizontally and less often than you think
As for mess, try and get a cage with a skirt on the outside, it will help keep some of the husks contained, however, yes they do make a mess and learn very quickly that something they find fun might upset you
have you thought about a canary or finches rather than a couple of budgies? a good, strong male canary can fill the air with endless song and are less messy than a single budgie, let alone two