The only limit is that Klauth's mana must be used on spells, not abilities, but that won't matter much in a typical Dragon deck
Phyrexian Tower Phyrexian Tower asks you to pay a real price for its mana advantage, but that price is often worth it
Im not entirely convinced that a 1/1 has all that much impact, but it can do a job against decks without Day of Black Sun
Creatures (6) Planeswalkers (15) 3 Karn, Scion of Urza 3 Teferi, Hero of Dominaria 2 Kaya, Orzhov Usurper 2 Liliana, Dreadhorde General 1 Kiora, Behemoth Beckoner 2 Teferi, Time Raveler 2 Saheeli, Sublime Artificer Lands (24) Spells (15) Oath of Kaya, Dreadhorde Invasion, Thought Erasure, and even Soul Diviner will hold off the early aggression while your planeswalkers hopefully stick around to start taking over
While most players are financially savvy enough to avoid making those sorts of mistakes these daysthank goodnessI still see plenty of people who operate under some pretty widespread misconceptions about how the market affects the games most expensive cards
1 Seal of Removal