As far as where is the best place to buy N-scale for less: ebay! But you must be patient and have a great deal of self control. People often get out of control when bidding, and pay too much for something. KNOW YOUR PRODUCTS AND PRICES!
As far as who makes the best N-scale equipment:
Loco’s: Kato, Atlas, & recent Lifelike. Kato tend to be pricey with limited quantaties. Atlas is much better with availability and price. Lifelike has some great recent releases at bargin prices (like the GP20, FA’s, and SW units).
Intermountain and MT have entered the Loco market with FT’s, and reports say they are nice units.
Rolling Stock: Much debate here, so I will offer more of my opinion than anything else.
MT (Micro Trains) is the “Cadillac”, and has been around a long time. They tend to command a high price, but some other manufacturers have caught up (and even surpassed) them in quality. MT also does not run multiple car numbers for any given release, and have the interest of collectors (which can affect price and availability)
Intermountain is on par with MT, including price. But they offer more unit numbers per release.
Red Caboose is supposed to be of higher quality, but I have no experience with them.
Atlas has been around as long as MT, and has some really solid offerings for a good price. But their recent releases are starting to get more costly as they improve their quality.
MDC/Roundhouse is good. Their older kits are a bargain if you can find them (usually on clearance).
Bowser is okay – but a bit pricy for what you get (still put Rapido couplers on their recent releases).
Deluxe is okay (from my limited experince).
Lifelike, Bachmann, Model Power, and Concor are lower end. If you don’t pay too much for these, and make truck/coupler upgrades, they can make decent running cars.
Industrial is ultra cheap all around.