In LotFP's silver standard, 1 gold coin is worth 50 silver pieces. If you want to tell me that a crown made of gold is only worth 500sp (or 10gp), then your definition of 'crown' had best equate to 'circlet', cause an actual crown made of gold absolutely has FAR more than 10 coins worth of gold in its construction. (As an example, here's a relatively plain crown made for Napolean) I would guess closer to 30-50 coins worth of gold. That would put the crown at about a 1500-2500sp value
This assumes that gold coins are only worth their weight in gold, which kind of negates the value in minting them in the first place. The ''gold'' and ''silver'' standards I think most people are used to dealing with would stem from backing currency with precious metals reserves, right? Is that what's really going on here? I think you'd more be dealing with coinage as an intermediary unit of exchange; if you'd trade two crossbows for a mule, then a mule should be worth twice as much as a crossbow when it comes to currency-based pricing.