I just finished up a D&D 3.5 dungeon crawl using HA, it went well (Im very glad I stuck with the walls being one block high in the hallways)

as for the cheapest way in. grab the basic fieldstone mold (#70) and afloor of your choice, that will give you a nice start, you will want to add on later

do not go the cheapest route when it comes to your casting material, avoid Plaster of Paris, instead use somethign stronger (I like Merlins Magic) otherwise you will be disappointed.

other than that you can use cheap house paint and brushes to add color (I also start with dark grey plaster).

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