Radiant Touch by YSL retails for $40 for .1 oz. While the product is amazing at highlight undereyes, cupid's bow, and nose, the price is a bit steep.
The closest dupe that I have found for this is the Revlon Skinlights Illusion Wand, which is .05 fl oz. This product is discontinued in the US but is available on sites like ebay for around 6-7 (I managed to find mine for $2 plus $2.50 shipping).
One of the main differences is that Radiant Touch comes in 8 shades, so it is much easier to match your skin with your desired highlight color, while Revlon Skinlights comes in only 4 shades. I purchased light touch as I have fairly light skin in winter, so the lightest color works best for me. It is easily blendable with your fingertips and offers a similar effect as Radiant Touch, that is a subtle highlight that is more of a sheen than a glittery shimmer.
Wear: Radiant Touch definitely lasts longer throughout the day, but for on the go touch-ups Revlon Skinlights is compact enough to carry with you. It is a similar applicator to the YSL version with a brush tip applicator and a twist to raise product knob at the bottom.
Rating (from 1-5): 3.5. I prefer the YSL Radiant Touch if I have the extra income, but for those of us trying to cut back our beauty budgets, this illusion wand is a great alternative. The packaging claims it will also double as a concealer, but other than under the eyes, I would not recommend putting this over blemishes as it does not conceal well for dark red spots.