Does 97 Avalon bulb fit in a 98 Avalon headlight?

Yes, they are glass instead of plastic though. This works for 98 model lamp assemblies installed in a 95 Avalon

Since you didn't include year in your question, I'll have to answer in general. It will vary depending on if you have HID or Halogen low-beam headlights (high beams are halogen on both versions). In...

these plugs should come ready to go double check but most toyotas require plugs with either 2 electrodes per plug or 4 electrodes per plug in which case these plugs are pre gapped for your engine...

I would try a junk yard. Often you can look for your make and model and they will charge you a nominal cost. try www.ebay.com