Oh, definitely not as much as 10x the castle and city budget, however that much is. But the Chief Builder doesn't really have any numbers like that planned, he's just hoping there'll be money there whenever he wants it. He's a construction manager, not an accountant.
Wow, her Supremacy really is from another dimension! Only Sparks can make weird machinery. Prudent Sparks can sometimes make it be the case that some of the parts are maintainable by trained normal minions. But there'll always be some Weird Science parts that occupy a sliding scale of "you must be a Spark at least this powerful and/or specialized in order to do anything with this particular weird subinvention". Whatever summoned Opalyn to this dimension, for example, probably the core of it was a bit of machinery that could only be built or repaired by Doctor Disaster or one of his direct rivals in dimensional mechanics; or by one of the great continent-bestriding Sparks like a Heterodyne or Storm King.