Hello!

First of all interesting deck! I hope it gets more attention around the site, as most people see mardu as just mardu nahiri decks and don't look at other ways of building the deck. I have some suggestions that are both very budget friendly and would improve a lot of your matchups against decks currently in the modern meta.

1. Cut a Night's Whisper and a Gurmag Angler and mainboard 2x Anger of the Gods the reason for this is because dredge and infect are very weak to this card, and is extremely good against the current modern meta that is centered towards aggro decks.

2. Cut the swiftspears and Soulfire Grand Master in favor of either more tokens like Timely Reinforcements and Mardu Charm and some planeswalkers. Such planeswalkers can inlclude Sorin, Solemn Visitor, Chandra, Pyromaster, Sorin, Lord of Innistrad The reason I say this is because the tokens allow you to play around the most popular decks in the format that can get around cards like Butcher or kill it (ex. Jund/Junk). Hero of Bladehold is another possibility for this.

3. I can tell that your mana base is budget, but I think you need to make some considerations here, Clifftop Retreat, Foreboding Ruins, and Dragonskull Summit are all great cards, but require you to be playing a mana base of shocks to support them, since you need the quality of the basic lands, which you only play 3 of. I'd cut these for either more fastlands or painlands like Sulfurous Springs.

4. In the sideboard I'd consider playing Slaughter Games over maybe anger and maybe a sin protector or something, as it lets you take out combo deck pieces without worry.

5. I'd cut gurmag angler for planeswalkers/ more tokens as you need to wait a while to cast it since you don't have a lot of graveyard filling.

You also might want to either add more lands or get cheap fetches, as 23 lands is what most lists usually play.

I'd probably cut a couple thoughtseize for more token producers.

Also Wear should be included as at least a one of in the sideboard.

Also I agree that this deck needs more lands, 19 isn't going to cut it for a deck that expects to be winning the game with 3-4 cmc cards and up.