I hope you have an agent to run comps for you... If not, I suggest you get one and your question is answered.

How much you offer is really 2 different questions: 1) how much will you need to offer to get the house and 2) how much you are comfortable paying for the home. 180 days is a long time - how long has it been at $145,000? That's a key question. If it's been at $145K for more than a few weeks it's still overpriced. Is it bank owned, short sale, or regular sale? If regular sale, how much do the sellers owe on it? What are the area comps for similar homes in the last 60 days max? These are some of the questions you'll need to have answers to (your realtor should be able to provide answers to these and other questions you have). Good luck!

there is no "magic" percentage to offer. It depends on the true market value of the property. Is it priced well, is it priced low??

It's important to know the value of the home in your neighborhood, and offer accordingly.