Ballpark would be hard without knowing what size etc.

But with a little research on prices you can get a good idea. Just measure the square footage you need for drywall and insulation. Add some footage for DW waste. There you go you have that cost.

Now figure out what you will need for electrical and where. Get a quote from electrician. Now you have that cost. Add in drywall mud and paint cost. Cost for lights you will be using etc. etc.

Just try and figure out all the stuff you will need and with a little time on a HD site you will have all your DIY costs.

Your electrical is the wild card. You can diy some of the electrical(drilling holes and pulling wires etc.) to save costs but you should have an electrician do all hookups. They are also great at pointing out things you may have not thought of. Most in the trade will work with you that way.

But remember it is ballpark. There will always be extras that you never thought of or say a structural issue you didn't know about.

You shouldn't have a problem getting a ball park. Just leave room for any unforeseens. One would be you find out mudding drywall isn't your thing so now you have to hire out.

Finishing a garage is pretty straight forward so your ball park should be close