The cheapest "try it out" option is gonna be one of the all-in-one packages you can get through places like Amazon, such as the
Venzo SPD Shoes + Pedals & Cleats, around $70 all in. There are a number of the shoe + pedal combos on Amazon, none particularly fashionable, but generally well reviewed, and as the OP requested, cheap.
Gone are the glory days of 20 dollar M520s. They're $30+ from Chinese sellers. Shipped from a domestic seller, $45 is pretty typical. Add in even a cheap pair of shoes are you're north of $100.