- Замок (Castle)

Actually, the Castle is not the most expensive in terms of any of the resources...

Town----------Gold--Wood--Mercury--Ore--Sulfur--Crystal--Gems

Castle---------111000---147-----42-----122-----42----47----42
Rampart---------106000---127----30------142-----30----95----45
Tower---------111800---135----48------135-----43----49----89
Necropolis----97400----145----40------135-----50----45----65
Dungeon------112400----142----40------142-----82----32----45
Inferno------115300---120----86------125-----51----28----36
Fortress-------92400---185-----29------105-----49----10---10
Stronghold-------92200---157-----10------152----10----60----15
Conflux--101 800---137-----65------140-----38----33----35

The cost of a fully built town, including the Mage Guild, is shown.

In my opinion, the table needs to be edited.

Town----------Gold--Wood+Ore--Gems

Castle---------111000------269--------173
Rampart---------106000------269--------200
Tower---------111800------270--------229
Necropolis----97400-------280--------200
Dungeon------112400-------284--------199
Inferno------115300-------245--------201
Fortress-------92400------290---------98
Stronghold-------92200------309---------95
Conflux--101 800------277---------171

So, what do we see? The cheapest towns are the Stronghold and the Fortress; yes, they require more stone and wood, but these are the easiest resources to gather.
And the most expensive town in terms of gold is the Inferno, but if you consider gold plus gems, then the Tower is also quite expensive. Well, the Castle is a solid middle-of-the-road option; it's certainly expensive in terms of gold, though....