Put money in thy purse; follow thou the wars; defeat thy favor with an usurp'd beard. I say put money in thy purse.
Rather than trying to devise some sort of elaborate pricing system, I try to map game world costs to approximately similar real world costs.
In my campaign the basic unit of currency is a small silver coin, called a klink. This coin is worth about $10.
A restaurant meal costs about 1 klink.
A room at an inn costs about 10 klinks.
Military style rifles start around $1000 and go up rapidly in price. Swords start around 100 klinks.
You can get a crappy car for a couple grand on Craigslist so you can buy a worn out mule for a couple hundred klinks. A new sports car will cost about $50,000. You can buy a war horse for 5000 klinks. If you want a Maserati horse, you can buy one for a Maserati price.
Prices vary according to quality and circumstance. Generally, you get what you pay for.