That's difficult to answer as the "lower" dollar amount may differ based on the size of the Business. Having said that, IMHO, for IT Hardware, the threshold could be $50 and the Accessories category may fall in there.
Also, just to share with you our approach, we set up Auto Receiving by Commodity Codes alone, without any dollar threshold. This is just to ensure that vendors providing the frequently ordered items are paid without delays. Any other items (commodity codes) not falling in this require manual Receiving.
Amina - We auto-receive requisitions and it has helped significantly reduce the invoice issues on low $ items.
The $ threshold depends on your company size, company policy for approvals and on how you categorize capital assets.