Just like the marketing 'department' of a startup SaaS calculates a Cost Per Customer, figure out what your on-boarding process is costing the company and adjust your salaries across the board to be competitive in that arena. If you're not being competitive - figure out why. Maybe you'll save more money in the long run by providing better leadership training that motivates employees to stay longer, effectively making your cost of on-boarding training worth it. Or, here's a shocker, maybe that training just sucks and you shouldn't put your employees through it anyways.

And if you cannot find a way to be competitive whilst doing so, just like employers have learned to be with health, life, pension, and leave benefits, then your company will sink. There are many professions that many seek employment solely because they don't have the capital to invest into themselves and their training. Why should one open themselves to the burden of both, if there's an alternative?