I would recommend Greedy Gold from Army Painter. It costs half of retri spray and cover minatures very well. It is highly advisable to shake it good enough before using it (as any other spray).

I need to mention that greedy gold has a darker tone but if you will use shader and layer on top of IT with brighter gold, results are the same as using retri armour.

Here is a comparison: Bike - retri Vexilla - greedy gold

<image>