Most people say every 90k miles for the timing belt. If you wait til the belt breaks, then your pistons can hit your valves & bend them. It's not guaranteed, but there's a good chance. Then you may as well shop for a new engine.

If you're already doing the normal stuff yourself, then I wonder what costs $400?? Maybe that's a timing belt & valve adjustment... Look in your owner's manual for the maintenance schedule. Maybe you can do a lot of it yourself. Or at least you can go to a mechanic with a specific list, instead of just saying "I need everything done"$$$