You have at least two choices.
First, in any case, interview Realtors. Ask their opinions. Get comps. And not just figures on what the house is worth today, in its present condition. But also what the house would be worth fixed up. That's important for you to know, even if you do sell it in as-is condition. So, you'll have a figure from the Realtors.
Second, multiply the after-repair value (ARV) time 0.65. Then subtract estimated repair costs. (The Realtors you talked to may have given you estimated figures. Otherwise, depending on condition, you might be looking at anywhere from $30,000-$60,000. But get estimates, if the Realtors suggest that, or they're not confident in their numbers. So, ARV times 0.65 minus repair costs. The number you come up with there is what many investors will pay for your property. You can find the investors by looking in your newspaper classified ad section, by checking on CraigsList, or looking for "bandit signs" (the "We Buy Houses" signs on telephone poles).
Now you have two numbers: The Realtors' estimates of what you probably could get selling it conventionally, and a figure for what an investor would be willing to offer. One advantage of dealing with an investor is that the investor actually purchases the property, and can do so quickly. However, the number you're offered by an investor may be lower than the Realtor's estimate.
Then you decide which way you want to go.
Hope that helps.