Size Shift (Medium-size --> Large)
Base rank 1
Medium-size to Large +1 rank
Heightened Strength (+8) +12 ranks
Lowered Dexterity (ad hoc –3)
Heightened Constitution (+4) +6 ranks
Natural Armor (+2) (Heightened Defenses) +4 ranks
Mighty Lifting (+2 ranks)
Always on: -3 ranks
20 Hero Points. Minimum 9th level (12 ranks in heightened strength)
A nice round number.
Mind you, it might be better to redo Heightened Strength as follows:
Heightened Strength (+6) +9 ranks
Super Strength (+1 bonus to hit, +2 effective strength) 2 ranks
Heightened Accuracy (+1) 1 rank
Same number of ranks, but now the minimum level is 6 (9 ranks in Heightened Strength).
20 points, plus a few points of Enhanced Vision or Scent, or something, and you have an ECL of exactly +3.
Edit: thanks Morrus for the pointer to Mighty Lifting