[giffc]

It depends on stage and context of product. In the earliest days, I think whoever owns "customer development" should also own the UX. It doesn't need to be beautiful, just good enough (that's where context of product comes in -- it defines "good enough" -- a product for engineers will have different requirements than one for grandparents).

The trouble with using free time from a friend is 1. by being free, it is harder to give blunt feedback; 2. by being a favor, you are beholden to their schedule, and can they really keep up with your pace of iteration and learning based on customer development? It can put strain on friendships.

So in the earliest days I say try to DIY unless you really don't have a design bone in your body. Use paper and Balsamiq to sketch, and examine what you like and dislike of comparable products.

You can always hire a professional designer later to come in and help once you feel confident that you are close to the right product for the right customer.