There are, as far as I know, no precise records of the cost or availability of swords in Judea in the early Imperial period. However, in pre-modern times, clothing was frequently the most expensive item a person owned, and a nice cloak could actually be sold for quite a bit of money. So, even if swords weren't particularly cheap, the money gained from the sale of a cloak could probably purchase one.

A stockpile of weapons would, as you say, rightly draw the attention and ire of the Roman authorities. However, let's look at the passage in question.

Luke 22:36-38 (NRSV):

36 He said to them, “But now, the one who has a purse must take it, and likewise a bag. And the one who has no sword must sell his cloak and buy one.

37 For I tell you, this scripture must be fulfilled in me, ‘And he was counted among the lawless’; and indeed what is written about me is being fulfilled.”

38 They said, “Lord, look, here are two swords.” He replied, “It is enough.”

Two swords are not exactly going to break the bank, nor are they going to draw a large amount of attention from the Roman authorities. Why, then, is two enough? Look at the reason why Jesus ordered his disciples to get the swords:

this scripture must be fulfilled in me, ‘And he was counted among the lawless’

Scripture requires that Jesus, as the messiah, be a rebel, so he orders his followers to bring him the implements of rebellion. But he only wants the bare minimum in order to be considered a rebel!

They said, “Lord, look, here are two swords.” He replied, “It is enough.”

One sword is for personal defense, two is, in the most technical sense, a stockpile of weapons.

OP, you may also be interested in /r/academicbiblical.