Comma before ᴀɴᴅ after "on average"? [duplicate]

As broad guidance, the normal place for a prepositional modifier is {S + V [+ O] + modifier} and this construction does not require a comma.

“… that the developed methods lead to 10% less costs on average.”

Other positions may be correctly adopted for emphasis, but these all do require commas:

“… that, on average, the developed methods lead to 10% less costs.”

“… that the developed methods, on average, lead to 10% less costs.”

“… that the developed methods lead, on average, to 10% less costs.”

“… that the developed methods lead to 10%, on average, less costs.”

PS I would use lower costs rather than “less costs”