buying a song from itunes no longer an option (?)

Where exactly are you looking for the song?

If you are under the "Browse" or "For You" sections in iTunes, then you are in the Apple Music catalog so no prices.

Make sure the "Store" section is selected from the options at the top, and look for the song there. It should then show a price and can be bought.

Don't click on the downward-pointing arrow next to the price button, click on the actual price