That's a really really variable question. With access to the stores that I have; I could probably do a heater, tank, filter, and substrate for about $20 - $30
You can get a 50lb bag of sand from lowes, home depot, or tractor supply co for $5-$10 depending on what you want
A small HOB
filter can cost you $10-$20 A sponge filter and bubbler can run you about the same.
Tank you can figure about $10 unless you want a designer tank
A heater can cost you from $10-$30 depending on how much you want to spend. You get what you pay for where these are concerned.
A light / hood will run you from about $15 - $100 depending on whether you want to do live plants or not.