Donald Trump complains about the cost of the Mueller investigation, as if the money isn't being well spend. But it actually is being well spent as we can see by the number of people who have been indicted so far.
The Growing List of Indictments in Mueller’s Probe of The Trump Campaign
Paul Manafort - Former campaign chair, was indicted on a total of 25 different counts by Mueller. His first trial ended in a conviction on eight counts of financial crimes. Before the second trial, Manafort struck a plea deal in September 2018.
George Papadopoulos - Former Trump campaign policy adviser, was arrested in July 2017 and pleaded guilty to making false statements to the FBI.
Rick Gates - Former Trump campaign aide and Paul Manafort’s business partner. Gates was indicted on similar charges to Manafort. In February he agreed to a plea deal, pleading guilty to one false statements charge and one conspiracy charge.
Michael Flynn - Trump’s former national security adviser, pleaded guilty to making false statements to the FBI.
Michael Cohen - Trump’s former lawyer plead guilty to 8 counts, including campaign finance violations, related to hush money payments to women who had affairs with Donald Trump. Sentenced to three years in prison
Sam Patten - Patten was a lobbyist who plead guilty to not registering as a foreign agent with his work for Ukraine.
Keep in mind, this isn't the whole list. There are also various people not actually in the campaign who have been indicted and prosecuted. And more to come I imagine.