Let's compare the some various versions of low-tech armor in GURPS.
Note, coverage of 9-10 also covers the vitals (17-18) in all editions.
3e Basic Set and Low Tech.
Bronze breastplate, covers areas 9-11 front only (torso are 9-10, groin is 11) with PD 4 DR 4; $400; 20 lb.
Steel breastplate, covers 9-11 front only, PD 4 DR 5, $500, 18 lb.
4e Basic Set, PD is dropped.
Bronze breastplate, covers 9-10, DR 4F (F meaning front only), $400, 20 lb.
Steel breastplate, 9-10, DR 5F, $500, 18 lb.
4e Low Tech
Bronze breastplate for torso (9-11) is medium plate, DR 6F, $10,000, 10 lb.
Steel breastplate for torso (9-11) is medium plate, DR 6F, $2,500, 10 lb; but is TL4 which should double the price for a TL3 character.
Bronze medium plate covering just the chest (9-10) is DR 6F, $3,750, 7.5 lb.
Steel medium plate covering the chest is DR 6F, $937.50, 7.5 lb.; which, again, should be double price at TL3 if such advanced metal is available.
3e calls mail "chainmail"
A complete shirt, covering the arms and torso (6, 8-11) PD 3 DR 4 is $300, 34 lb. including the padding. Chainmail is PD 1 DR 2 vs impaling weapons.
4e Basic Set
Mail hauberk and sleeves (8-12) DR 4/2* (lower DR vs crushing, * means flexible) is $300, 34 lb.
4e Low Tech
Fine mail covering arms and torso (8-12) DR 4/2* (lower vs crushing) is $1,350, 22.5 lb. Adding padding is a matching shirt of padded cloth armor for another DR 1*, $60, 7.2 lb. for a total of DR5/3*, $1,410, 29.7 lb.; but DX -1!
Going with Low Tech is a significant saver of encumbrance, but harder on the wallet. The GM is the arbiter of which list the player uses.
Considering that the players almost always want an esoteric weapon only found in Low Tech, they kind of open up that can of worms themselves.
The biggest drawback of using Low Tech is you have to sit down and figure out what kind of armor you want over what hit location, and it can get VERY detailed. It can also be quite simple.
Low Tech's big advantage, in addition to weight being better, is you can configure your armor exactly how you'd want it.
For example, a short sleeved mail shirt is very common. This covers the chest, shoulders and upper arms (8-10, 12) but the armor only protects the arm if a 5 or 6 is rolled on 1d. The heavy mail version is DR 5/2*, $1,140, 17.1 lb. (DR 6/3*, $1,188, 22.8 lb., DX -1, with padding) Fine mail drops to DR 4/2*, $855, 14.3 lb. (DR 5/3*, $903, 20 lb., DX -1, with padding).
Scale armor was about the best bang for your buck in 3e.
Torso coverage (9-11) is PD 3 DR 4, $420, 35 lb. Plus arms is $630, 49 lb.
4e Basic Set is DR 4, $420, 35 lb as well. Plus arms is $630, 49 lb.
4e Low Tech medium scale DR 4 is $550, 28 lb. Adding arm coverage comes to $875, 42 lb.
A short sleeve medium scale shirt similar to the mail shirt above is DR 4, $523, 26.6 lb.
You can't make the short sleeved, short shirt with the 3e or Basic Set rules!