Hi splinters,
There are many new players coming from YGG and I would be glad to share my experience from the gold league perspective (+silver tournaments/ bronze & novice brawls),
While it is true that you have to invest to have a good deck, there are some underrated cheaper cards that you can sneak from the market for cheap or rent out.
Today`s pick is Gelatinous Cube - this monster has no attack, but it is insanely attractive in a low mana cap. When you know that your opponent has little to no damage - you will just outheal them to death. GC has a scavenger ability, which adds +1hp for all the dead monsters on the battleground and an in-build heal.
https://splinterlands.com?p=battle&id=27281dc5d75bc5278172c75b4e3af89ad04bebdb&ref=masq
In the battle against 
Gelatinous Cube will be especially powerful in the following rulesets:
- Earthquake (non-flying monsters take 2 damage at the end of each turn)
- Noxious Fumes (all monsters start a battle with poison [-2hp at the end of each turn])
Now, how much will it cost one to get a GC lvl 6 (you can go for lvl 8 if you have extra funds) = $0.21 * 52 copies = $10.92
A great investment that will pay off in no time! Careful, some enemies might be really upset to see the wall that they are trying to heal but just miserably fail.