Buying Kilts
I get my kilts online at Sportskilts.com. For kilts they are cheaper than most. They sell most of the other things you want to go with the kilt. They do some custom things like if you want pockets or not and how big of belt loops you like to have or no belt loops on the kilt.
If you're wanting something that has the look and feel of a regular kilt for half the price, Stillwaterkilts.com has an Economy kilt that was around $50 when I bought one a few years ago. It's velcro so it's easy to take on and off. It's also machine washable. It's made out of an acrylic fabric so it's not a "Real" kilt but if you're wanting to try one out, but not spend a lot of money, that is the way to go.
Otherwise, the ones they already said all are great websites as well.
Be careful, most cheap kilts are only 5 yards or less, and made very thin acrilyc material, so not heavy enough for outside wear, except on sunny windless days. Many of the Asian sellers, claim to sell 16oz 8yard kilts, but again, the whole kilt won't weigh 16oz, and most likely no 8 yards, but 5 or 6 yards. Polyviscose kilts are better. Weight more than acrylic, and don't itch like wool, inexpensive, and machine washable. They don't last like pure wool kilts, but they're about a tenth of the price!
I bought one for14 GBP. It is of a proper woollen tartan and well pleated. They must have been popular as the size I ordered had sold out. I was sent a size larger. It did have one particularly amusing aspect. When I pulled my tummy in it instantly fell to the ground. What a way to show I had nothing under it! Alas that was not too practical so I have taken it in a bit (spoilsport!!!).