As all of the values cited below are shown in pounds (£ from liber), shillings (s from solidus) and pence (d from denarius), we should first clarify the break down of English currency at the time. It is also important to note that the pence or penny was worth less (240:1 £) than it is today (100:1 £).
1 pound (£) = 20 shillings (s)
1 shilling (s) = 12 pence (d)
1 pound (£) = 240 pence (d).
The armour owned by an unnamed knight in 1374 was listed as £16 6s 8d. The armour in the house of Thomas of Woodstock, duke of Gloucester, in 1397 was worth £103. The value in 1441 of a suit of Milanese ready-made (munition) armour was £8 6s 8d, and a set of squire's armour was £5-£6 16s 8d. And, in 1614, a suit of armour "gilt and graven" belonging to the Prince of Wales was valued at the incredible sum of £340.
So exactly how much would that be worth today? Fortunately, antiquarians have spent a great deal of time and energy trying to come up with formulas to ascertain the value of the proverbial dollar throughout history. The most simple method is to take the basic daily wage of a common laborer and compare it to the current minimum wage. That will give you a basic understanding of the present day value of a Medieval price tag. More extensive formulas have been developed that consider multiple factors such as the price of wheat and bread as well as the wages of both skilled and unskilled laborers. The result has shown a much more accurate analysis of the modern day equivalent to Medieval wares.
Using such a formula, I converted from the American dollar to the English pound using historical currency rates for the month that I made the initial deposit on the commission. While I will not say exactly how much I paid, I was able to determine that I would have paid £13 6s 11d for my armour if I had purchased it in the year 1450. Surprisingly, that is very much in line with the historic cost of armour in extant documents.
Now consider the fact that a suit of armour was surprisingly only a relatively small portion of the overall cost of outfitting a knight for battle. The greatest expenditure was to equip him with a highly trained warhorse, which could cost as much as £80. He would also need to be equipped with weapons such as a sword, lance, pollaxe, and dagger for battle. He would need a riding horse, pack horse or draft horse and wagon, tent, attendants, retainers, and all of their supplies. In today's dollars that would be the equivalent of hundreds of thousands of dollars plus regular wages.
[Sources: English Weapons & Warfare, 449-1660, A.V.B. Norman and Don Pottinger, 1992 (orig. 1966). The Armourer and His Craft From the XIth to the XVIth Century, Charles Ffoulkes, 1988 (orig. 1912).]