Buy cubic zirconium then, it’s the cheapest artificial gem which is still jewellery grade (though on the lowest tier, just above high quality glass).
I’d bet you can find them on ebay and if that fails, google a jeweller supply shop in your country. They are very common and affordable.
There are artificial rubies and other gems which aim to mimic the index of refraction of the real gems, they are much more expensive and they exist in different types, but, they are still cheaper than the real thing.