Comment by dspillett

This is one of the reasons 3D printers are becoming a lot more common in homes not inhabited by the sort of geek/nerd like me who you would (correctly) assume owned a 3D printer or two.

Yes, something you print yourself will likely be lower quality than a bought one from years ago and you'll pay more in material and time than buying a new one will cost, but... it may be no worse quality than a new bought set, possibly better, replacement parts can be reproduced easily or additional parts added to the set cheaply (no buying a full set to get a couple of extra pieces that you want) and things can be customised.

One of the bigger 3D catalogue sites (I think MakerWorld, but without checking I'm not 100% certain) ran a marble-run themed contest some months ago for which there were a lot of interesting entries, some just copies of basic parts/sets (great if that is what you are looking for) but also some that were more innovative than that. If you have a printer, or know someone who has, it might be worth you looking into that if your kid would appreciate a new set, there are a lot of free designs¹ out there you could experiment with.

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[1] and paid ones, some designers try to make a living this way and some of them produce designs that are well worth the cost as they may be free of issues more amateur designs could have