れれっ？ 本当にないっすか？ んー、おっかしいなぁー
It's a conversation from video game, one of the characters is surprised by the answer of his companion.
My guess it's something like "Huuuh? Not really? Hmmm, strangelyyy"
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It sounds like an intentionally odd or silly rendering of あれれ？, which is itself a mildly exaggerated version of あれ(っ)？, a normal expression of surprise.
Your guess about this is correct.
The rest of your guess is actually a bit less so - 本当にないっすか is 'is it really not there?', and おかしいなー is closer to 'that's strange' (it's not an adverb).