In terms of price, Cavern of Souls goes for around $50 at the low-end of sales, but the card is starting to uptick towards $65 in both versions
There are tens of thousands of lifegain decks spread across mono-white, Orzhov, Selesnya, and more color identities
The Indomitable Just casting The Indomitable and attacking with a creature or two is already a profit
It has all the advantages and problems as Luminous Bonds while gaining flash and shutting down Convoke and tap ability for the cost of an additional mana
However, if your mission statement as a casual player is play as many unique and enjoyable games as possible, then at least having an open mind and a 1v1-oriented deck will lead to playing games you otherwise wouldnt both in how those games play out and the actual literal opportunity to play them
It doesnt let you ignore format legality