Must the products be at the $50-$100 range though. Is there a reason for this?
It's not 50-
100, he actually said
50-1000 in the OP:
Products in the $50-1000 range on Amazon.
Reason is obvious, to get more commission from less number of converted sales, and may be the buyer will also buy some more related or even unrelated Amazon items along with the item link he has clicked on, and you get still bigger commission for that.
Compare this:
Please refer to this image:
Suppose:
Case 1:
In a month, you sell 1,000 quantity of a $10 item (total sales: $10,000) :: You get $800.00 (@8% per item as per the image above) commission.
Case 2:
In a month, you sell 50 items costing $200 each (total sales: $10,000): You'll get $650.00 (@6.5% each) commission.
If you sell another 12 (total units sold: 62), then the commission rate will be the same 6.5% (refer the table), and your 62 sold units at $200 each unit will cost $ 12,400 and your commission amount at 6.5% will be $802.00
~~~~
The difference is in the selling units: to earn approx $800 in a month in Amazon commissions, you sold 1,000 units in the 1st case, while you sold only 62 (whooping 938 items fewer than in the 1st case) items in the 2nd case.
I wouldn't worry about who the hell will buy the "costly/expensive" $200 item on Amazon.com. May be that $200 is still a good bargain price on Amazon compared to the offline stores' prices for the same item. So many people who need the item will buy on Amazon at that price... Availability (or lack of it) of that item in the buyer's locality is another factor which drives a sale... Convenience and ease of buying is yet another... ease of returning it could be yet another, sellers on Amazon need to be at their best behavior 24x7,

because the consequences of being unpro, negligence, being "scamy", or displaying rudeness will be worse compared to the offline scenario....... Safety for the buyer is The Keyword here

!
There absolutely are US buyers who buy items which are lot more costlier. It's up to your affiliate site to get their eyeballs to your affiliate products, and then to make them buy them (some of those aff products) over the rest of the competing sites that matters imo.
Another advantage:
Your visitor/buyer may buy more items along with the product you've advertised on your site, and that means more $$s in commissions without advertising for those additional items he/she buys that day!
All that needs work, but it helps to learn about such things too.
HTH.
P.S.:
btw, that $800 is a great amount in local currency for most of the countries in the third world. In India, for example, the $800 is more than INR 50,000 (before taxes), and it can bring a good lifestyle for the earner, and doing very little extra work on a site that earns him $800 p.m. on autopilot on Amazon.