Currently BM offers a custom grip in 154CM standard, n680 +$15, D2 +$15, S30v +$20.
To Benchmade, S30v is their hi grade steel. D2 is the most difficult to maintain. REI is the most expensive retailer to purchase knives from, then Cabelas. If you are dead set on a grip, check out the Knife Exchange forums. I picked up a custom grip with 154m never used custom scales, clip, blade type $110 from the For Sale by Individuals sub forum.
Your question has great interest to me as last month I hosted a custom grip GAW. Each day members chose a seperate knife component from the Benchmade website. Blade type, Steel type, Handle color, etc. Overwhelmingly, steel choice was the most voted on, controversial, and commented on of all the components. Hands down S30v was the clear favorite among the regular members of the particular forum I ran the GAW in. All told the final product was $179 delivered, factory direct, in S30v.
So for under $180 you should be able to get what you want.
Keep in mind a Griptilian is considered a $150 knife. If you find one you priced lower than that you might jump on it. I've seen them new for $130 & as high as $165. Just depends on where you shop and how deal breaking +/- $10 is?