well there is a glitch to have infinite budget, but it is very specific in what you have to do.
1) Start a BLANK (absolutely nothing on it) canvas (sorry, you have to start all over again!)
2)Create one of every object, besides spawners and goals (like the flag) (make a big pile in an area you won't use)
3)While you are spawning all of these, press X twice on each of them to open up a menu, and from there change all of their "Run Time Maximums" To the highest number.
4) Once you run out of budget during this process, Save, Quit, and start the map again. Keep doing this until you have one of every object on your map, and they all have Run Time Maximum at the highest it can go.
5) Once you have them all, save, quit, and start again.
6) Now you can start building your map, and once your budget hits 0, you can still build!
7) When you are 100% done your map, save as 2 new maps (one for editing stuff, and one for playing)
8) Open the map that you saved for playing, and delete all unwanted objects. You can now no longer edit your map, but at least there is no pile of junk in it!
NOTE: DO NOT DELETE ANYTHING! IF YOU DO, YOU CANNOT SPAWN ANY OF THAT ITEM AGAIN! JUST PUT UNUSED STUFF IN A CORNER