Some gameplay tips:

Recommend the places to farm the runes:

First Countess in Hell difficulty. She drops runes every time. But the highest rune she drops is 24#. So it is only suitable for farming lower runes.

Hellforge quest (Quest 2) of Act 4 are main source for runes too. Nightmare highest rune bonus is 22#. Hell difficulty bonus runes are 15#-25#. Farming this quest is called Rune Run. Some people specialized in Rune Run (RR for short) usually use RR to get the runes to synthesize higher runes.

There are quite a few People like farming runes from farming secret cow level in hell difficulty. It is said that the highest drop is 31#.

K3C (Farming unique High Council Members in act 3) is also a great rune hunting method. It is said that the highest drop is 33#. Blessed Hammer Paladin is the fastest.

Finally, the drop rate of the runes from Hell Baal is also considerably good.

[D2R Ladder] #30 Ber Rune
$0.55

[D2R Ladder] #31 Jah Rune
$0.55

[D2R Ladder] #24 Ist Rune
$0.75

[D2R Ladder] #26 Vex Rune
$0.25

[D2R Ladder] #33 Zod Rune
$0.25

[D2R Ladder] #28 Lo Rune
$0.29

[D2R Ladder] #23 Mal Rune
$0.55

[D2R Ladder] #32 Cham Rune
$0.15

[D2R Ladder] #22 Um Rune
$0.09

[D2R Ladder] #29 Sur Rune
$0.29

[D2R Ladder] #15 Hel Rune
$0.05

[D2R Ladder] #21 Pul Rune
$0.09