Some increasingly convoluted steps to get 21, a new best for me:
1: $4 -> Nomad camp
2: $3 + Nomad camp -> Watchtower, Hamlet (draw e, shuffle, draw all actions and c)
3: Play Hamlet, discarding e and c, drawing c; play Nomad Camp, then Watchtower, drawing 5 c; buy Crossroads, Tunnel, Develop (ee left on deck) - draw ee, shuffle, e, tunnel, Crossroads
4: Play Crossroads, drawing Hamlet, Develop, Nomad Camp, and Watchtower; play Develop, trashing Nomad Camp, topdecking Vault and Develop; play Hamlet, drawing Vault, discarding tunnel and e, topdecking Gold; play Vault, drawing Gold and Develop, discarding e and e for $2; Develop Gold into Bank+Horn of Plenty; play Watchtower, drawing Bank+HoP+4c, play 4c+Bank($5); play HoP, gaining Province; buy Colony
Phew, that's enough thinking for today. 8P