Proper garden containers can be expensive. One of the cheapest ways to get round this is to not buy 'proper', but to use something else (as Shedmistress said). Or, in the vintage / recycling parlance, 're-purpose' something else.
Scout round cheap places like charity shops or car boots and try to see things with a new eye. Use PP's mantra of "anything can be a planter".
You can make things look a bit more cohesive, if you want, by giving them the same finish - a lick of paint, faux stone effect, etc.
Alternatively, get busy with an old pallet, plastic liner and your carpentry skills.
As ever, Alexandra has a handy video on this.