Do you have a good resource for current avionics values? .
None of the resources you want actually exist. To have efficient markets and good information requires lots of sellers and lots of buyers in a full disclosure mode. Think of places like the New York Stock Exchange. Everybody knows what the last trade price was.
Even cars, for a bit have a "blue book" just because there are thousands of each model of car being sold, each month. But, start looking thru the back of a BlueBook for cars (NADA) and you will find all sorts of adjustments. The price of a Camry in Florida is different than the price of a Camry in Wisconsin which is different than the price of a Camry in Calif.
But, to continue with the car book, look at the prices, you will see a Low book of $8600 and a high book of $10,400 on some model. that is a pretty big range. Then consider the actual car was driven by a businessman and maintained by his company vs. the same car that was driven by a soccer mom and had 800 meals served to kids with soccer cleats in the back seat while running to practice and forgot oil changes.
Unfortunately, for planes, the volume of 1964 Cherokees getting sold this month is a small number. There isn't enough of a market to get accurate information. And, that plane in Florida had a different 50 year life than the one in Seattle. The one that spent 2000 hours being a trainer spent a different life than the one that spent 2000 flying the elderly Dr. around with his wife.
So, people start giving estimates, ranges, guesses. And that is what you are going to have to do. Start making a spreadsheet of all the planes in the model you want as they get listed on TradeAPlane, Ebay, Barnstormers, etc.
Track engine, total time, engine time, location, and, if you care, some sort of avionics (IFR vs non-IFR would be enough for me) and Asking Price. Start sending emails on ones that might be of interest. If they are out of the price range, ask them "Would you consider $xx,xxx if I paid for a pre-buy and no major issues were found"? If they say "no", move on. If they say "yes", you have a data point and a possible plane to continue.
Eventually, your spreadsheet will have 12, 20, 30, 40 airplanes, and you can start drawing conclusions on pricing, and factors affecting value. You will have to assign a "value" to Asking prices that are nonsense. But, if you stay with it, and you keep it updated as planes get listed, you will find the overpriced planes stay on TradeAPlane for months, the fairly priced ones seem to always "disappear" after a short time.
The only way you are going to get the information you seek, is to go get the information yourself. You might pay a Buyer's Agent, but, unless he is an expert on the plane you want, he will be doing similar. (Likely a big part of his efforts would be contacting his Contact List of Brokers asking if they have a BugSmasher -180 or know of one.).
As far as Avionics, I don't know that you should value them much at all on a single engine plane. What was "valuable" and state of the art 5 years ago is old. 10 years ago is ancient. 20 years ago is prehistoric. I am sure there are a lot of sellers that want to get their money back for them, but the panel differences would be the last thing I would give credit for as I could put in whatever I wanted much easier than replacing an engine or replacing an airframe.
And things like "hail damage" and other items only affect the value if the buyer's say they do. The fact that you are asking about it means that it causes some concern to you. All things equal, the plane without damage is more valuable than the one with damage. If the guy knocked $500 off, would you jump on it? $1000? $2000? $4000? etc.... Just keep in mind, when you go to sell it, the next buyers will also wonder if they want an airplane with hail damage, so, they might expect it to be $1000, less, $2000 less, $4000 less, etc... ANY item that causes you to question the value as a buyer, probably means it does affect the value, to at least one buyer, you.
People have given you good advice, but you eventually have to take the step to become the expert on the model you are buying, because, at the end of the day, your money, your time, your enjoyment. A few hours a month with a spreadsheet and google would quickly make you the expert.
Good luck.