Don't buy a $800 cream, that's insane! Urea is a common moisturizer ingredient, and there are many reputable brands of urea on Amazon:
You likely won't see much difference between 30% and 40%, in my opinion.
There are some combination creams. Topix sells a product called Glycolix that's 15% urea and 15% glycolic acid. Studies have shown that urea works even better when combined with salicylic acid, and glycolic acid should be similar. It's also sold under the brand name Replenix, for some reason. It's a bit expensive, and I've not tried it, but it should be good.
See our descaling guide for more.