well as you already said you are hating to spend the money but from the bottom of your heart you know what you require - ROOT CANAL
about the xray i have to say that it is not rare because dental decay
is usually like this what appears on top is just like the tip of an iceberg. the decay is much greater inside. so trusting by your hygienist who should not be doing a root canal you require a root canal.
however you can delay it with painkillers if it pains , but keep the area very clean.