So far, I've only seen replicas (some say they are actually the non-branded version of the boards, not replicas) of the ARB for around $300 (some people complain the bolt holes don't line up in some places, but even the stock ones do that a bit until you shimmy the bolts into place). The SRB only provide steps for the rear passengers. Most folks will tell you that the ARB don't help much and they just rub against your pant leg. This depends on your height I suppose. My 5' wife loves the ARB, but I know others the same size that don't use them because they're too close to the vehicle body.
I bought my Advance Running boards on Ebay for $400 shipped. They are incredibly easy to install and I think they improve the look of the MDX immensely. That said, they are of limited utility for me and they are only really used by my kids when they are getting in and out of the car, or when someone is sitting in the 3rd row and trying to get out. I actually like that they don't stick out like other running boards and haven't gotten the dirt marks on my pants like I do getting in/out of F150 or Durangos with running boards.
If you're planning on driving in the snow keep in mind that running boards decrease already low ground clearance. As far as utility, just like the other member mentioned, they're suitable for someone with tiny feet. For an average adult they will be more of an obstacle, IMHO.