www.digikey.com and
www.mouser.com and
www.newark.com are probably the largest distributors in the US.
Digikey started out repackaging stuff in smaller quantities. Before digikey existed it was tough to find a 1% resistor without buying 100 of them.
With a lot of parts, you can buy each or "cut-tape", reels, or digi-reels. You don't want a digireel or a reel. I once ordered one part in the digireel form by accident. That tacks on about $10.00 to the price.
Some places may sell totally based on quantity. e.g. <25<x<99 $1.00 where others might have prices like $0.90/ for 1 to 10 and $10.00 per pkg of 10 so 25 will cost you 2*$10.00 + 5*$.90.
Your always going to pay about $6 (Priority mail) to $10 (UPS ground) for shipping, BUT WATCH OUT for backorders. It can eat you out of house and home. Shipping complete is a way to minimize those costs. Other options are available too.
Some companies have arrangements with say UPS which means that's their preferred shipping method or their only shipping method. It also means you get the stuff faster.
I deal with a non-electronics distributor sometimes that has a unique method for shipping. I ordered 4 items where 3 were similar. The items came from 3 warehouses in 3 states. The main warehouse is in a 1 day zone for UPS. The other's were at least 3 days away. With this company, you only pay one shipping charge, so the ~$10.00 max charge was apportioned based on the dollar amount form the warehouses. Otherwise, it could have cost ~$30 or so to ship 4 items.
Some still have minimum order amounts and if you don't meet them, you have to pay a handling charge.
Quantities usually aren't the problem. Shipping, time and availability is.