There are lot of options for using money for first let's say 10 turns +/-.

Usually you got 100$ + maybe $200-600 from tribe + $200-400 for trade = around 700$ +/-

Often, what are your choices?

1. Buy Military (gun/horse/etc.)
2. Hire Immigrant (quicker to obtain more immigrants)
3. Hurry Building (e.g. for food, defense, storage, cross, etc.)
4. Rush Soldier/Cannon (either buy from King or from europe)
5. Trade with Native to Earn More Money (with FINALIZATION goods i.e. no raw material, and native prefer gun/horse/tools most the time)
6. Other (e.g. save money to rush privateer)

there is only one option: keep trading

As long as your indian tribe has money you should try getting it, so:

Take guns and tools, sell to indians = 900$, now you have 1000$, you buy 100 or 200 horses, 37 guns and maybe a dragoon, then get all money from indians and make rush (or defense)