Supposedly the Democratic Party spent $24 million in GA-6 election (I saw larger and smaller numbers).  They lost.  The party count in the House of Representatives is 238 Republicans and 193 Democrats (there are 4 vacancies which I will ignore).  To regain control the Democrats will need to turn over 23 seats.  23 seats * $24 million = $500 million (rounding off) and that might not be enough.  That will be a lot of fundraising.