Gold-Efficient Items Greater than Their Parts

Many items have patterns that "create" the bonus feature of the item.  However, others are made up of individual components, and may have an effect greater than the sum of their parts.

Efficient Dota 2 items:

Boots:  Tranquil, Power Treads, Arcanes

• I won't get into these, but know that upgrading boots is always efficient.

Oblivion Staff:

Components:  Robe of Magi, Quarterstaff, Sage's Mask
Component total:  +6 Int, +50% mana regen, +10 Attack speed, +10 damage
Assembled total:  +6 Int, +75% mana regen, +10 attack speed, +15 damage
Net gain:  +25% mana regen, +5 damage

Rod of Atos

Components:  Staff of Wizardry x 2, Vitality Booster
Component Total:  +20 Int, +250 hp
Assembled total:  +25 Int, +325 hp, +on use slow (60%)
Net gain:  +5 Int, +75 hp, +effect

Scythe of Vyse

Net gain:  50% mana regen, +Hex effect

Aghanim's Sceptre

Net gain:  +ultimate upgrade only (no stat gain)

Monkey King Bar (MKB)

Components: Javelin x 2, Demon Edge
Component effects:  2 @ 20% chance of 40 dmg, +21 x2 dmg + 46 damage (total +88 dmg)
Assembled effects:  +88 dmg, +15 atk spd, +true strike + mini-bash 100 dmg
Net gain: +15 atk speed, bash damage +60.

Sange & Yasha (S&Y)
Components:  Sange, Yasha
Component Effects: +16 Str, +16 Ag, +15 Attack Speed, +8% movement, +10 damage, Lesser Maim
Assembled Effects:  +16 Str, +16 Ag, +16 Attack Speed, +16% move, +16 damage, Greater Maim
Net gain: Greater Maim, +6 Damage, +1 Attack Speed, +8% movement, +10% proc on maim, +6/3% slows on maim.

Hard-to-evaluate items

Ring of Basilius (changes % mana regen to flat mana regen)
Shadow Blade (Shadow-effect is modified from ring)