If you opt to work with a buyers agent, then ask that agent to give you a broker's price opinion. Although that's technically neither an inspection nor appraisal, it should give you a pretty good starting point if you don't already know that property and neighborhood it's in. Also, you could order an investor's inspection and appraisal to give you a more precise idea of what's the property worth right now (and after it's repaired).
Armed with that information, then write up your offer, and present it. That seller has 3 options: to reject your offer, to counter your offer, or to accept your offer. If that owner agrees to your price and terms, or if s/he is willing to counter then roll with it. Otherwise, roll with the punches, and move on to the next deal.