Yesterday we started with the “actual” lands that will help you cast the few Legacy spells, which are actually not free for some awkward reason. Back in the day deck lists always started with 4-ofs of the respective dual lands and then had to be filled with City of Brass or other painlands. These days are of course long forgotten by now. 3-colour and even 2-colour decks can use less than four of their respective original dual lands, because of the fetchlands acting as virtual duals. For most Legacy decks the preferred ratio is 8 to 10 fetchlands, while using only around 6 dual lands. The rest of the lands (you should only use between 18 and 23 lands in total, unless your deck is called “Lands”) are basic lands and lands fulfilling special roles for the deck instead of casting spells. The most frequently used special land is Wasteland, which is often used as a 4-of in aggressive decks to leverage their early game tempo into a win. White decks usually integrate a single Karakas to hate on opposing legendary creatures, especially the large ones, which somehow tend to always get into play without being cast for their real cost. The few decks that dare to use a win condition costing 3 or 4 mana deploy Ancient Tomb and to a lesser extend City of Traitors to get there a little faster. Various man-lands like Creeping Tar Pit and other very deck-specific lands can be found in the remaining land slots.
How do you start playing Legacy without going bankrupt? Of course there are successful single-coloured decks as well. Burn is probably the cheapest of those, as it doesn't fill its undemanding mana base with expensive special lands, like Mono White (Death and Taxes) or Mono Blue (Merfolk) do. Despite being the cheapest entry point, I would suggest a different approach. I would pick one of the many blue based decks, ideally the one you like best on paper or the one with the most Modern cards you already own, because you can keep using many of your cards, when you decide to switch to a different deck. You should already have bought Polluted Deltas and Flooded Strands by now (as they have started their inevitable ascent recently). Use those if the decklist you are copying lists Zendikar fetchlands instead and you don't own those (which you should not, as they are continuously losing value until their expected reprint). The tiny advantage of running the “right” fetchlands is not worth the price difference, as they are just better at getting a specific basic land. You could also just buy one of each required original dual land and fill the rest with the respective shock lands. Being able to fetch the one Volcanic Island for no damage is a very significant advantage, while later in the game you might be fine with fetching Steam Vents coming into play tapped. Maybe in a few games you will have to take some extra damage from Steam Vents, but at least your wallet did not take that much extra damage from the additional Volcanic Islands.
If you are just looking to invest into Legacy mana bases, but without tying up a lot of money in very few cards, the Khans of Tarkir fetchlands are the best plan, as they are staples in every format and will also become more important for Standard after rotation. In that price category I also like Ancient Tomb not because of a specific recent trend, but because it is quite cheap for a card with the pretty rare ability to provide more than one mana per activation.
See you in Rome, or check out the MKM series live coverage over the weekend!