I mostly used Mylor Crawling to reach Bronze II (Power Restrictions).
Summoner - Mylor Crawling
1 - Flesh Golem / Unicorn Mustang
2 - Failed Summoner
3 - Wood Nymph
4 - Goblin Sorcerer / Goblin Thief
5 - Earth Elemental
6 - Child of the Forest / Chicken
There are more combinations but this is one of the more affordable.
Cards to Rent
1 - Mylor Crawling (level 1)
2 - Wood Nymph (level 1)
3 - Chicken (level 1)