This fails to deal with issues such as exchange rates, local availability of materials and skilled labour, demand and previous stockpiles. Now a good GM can adjudicate these, and often does..so why have the large and bulky charts at all?
I don't. Piecemeal uses the "dollar system". In this coins are assigned a theoretical modern "dollar value". Any time you go to buy an item you base its price upon the value of its modern day equivalent.
Buying a sword is thus akin to buying an assault rifle. If we go with a copper coin being $1 a sword thus can cost somewhere around 20 gold (depending on ALOT of factors, in same places as little as two). A riding horse is a car, a war horse a Humvee. A suit of carefully designed plate mail is much like a tank, a suit of mail an armoured car.
Now difficulties still arise, misjudgements and the like. But it allows for a lot more "fast and furious" bargaining and haggling with merchants too. After all, things don't have price tags on them. Every price is negotiable, some merchants might refuse to sell if you don't haggle (thinking something suspicious is up, like maybe the item is worth a lot more than previously thought)