This is a very, very difficult question to answer
because it depends on how far back you start from and how far forward you're planning to go.
Did you get some manuals? Plan on two to four manuals ($40-$100). Lyman's and the ABC's of Reloading seem universally recommended, and you will probably want something from your bullet or powder maker to get their load data.
Do you have a workbench? You can't reload off a kitchen table, as a rule. A good, solid bench with shelves and drawers weights 150-200 pounds and is typically $300 (you can make your own for less than $100, of course). Do you need more light on your work area? Is there an electrical outlet close by? Have you got a comfortable stool to sit on?
Do you already have storage bins, shelf space and basic tools? Boxes and trays for your cartridges? You'll likely need good quality measuring tools (caliper and balance): don't trust your firearm's safety to cheap $20 calipers or a kitchen scale! Plan on $150-$250 on tools. Don't forget a bullet puller ($20-$30) and a powder funnel!
You'll want to prepare the cases. Dry media tumblers start around $80, wet media (stainless steel pins) are getting very popular I hear (they get great results) but cost around $300.
You'll need trimming, chamfering, deburring and cleaning tools for the cases and/or primer pockets. Lube for bottleneck cases. Depending on bells and whistles (manual tools vs powered tools), plan on $40 to $250.
What kind of reloading are you looking at? Will you be making large batches of good-enough handgun ammunition? Small batches of very consistent precision loads for a long range rifle? Shotgun shells? That determines the kind of press you'll need. You can usually reload most handgun and rifle cartridges on the same press. Shotgun shells require their own reloading press. Single-stage presses are cheap and slow, you reload in batches ($150-$200), one operation at a time. Turreted presses are a tad faster and costlier: you still reload in batches, but the setup between batches is much faster ($200-$300). Progressive presses are fastest and costliest, they're like a mini-assembly chain that perform multiple operations at once ($500-$700 without motorized accessories).
Whatever the press you chose, you need shell holder plates ($10-$40), and dies ($50-80 per set). Some shell holders fit multiple calibers, the dies are usually specific to a single caliber/case/shell size.
Progressive presses usually include a priming tool ($30-$40) and powder measure/throw tools($50-$100). Plan on buying them separately for turreted and single-stage presses. Plan on different priming tools for the different primer sizes. A powder trickler is practical but not mandatory ($20-$100).
Will you be annealing your brass to prolong its life? Will you be casting your own lead bullets? Will you be making wildcat cartridges? Those are entire new set of tools for each application.
So, to conclude: approximate cost? Anywhere from $500-800 for the simplest of setups (see Jethunter's post) to $1500-$2000 for a progressive with a complete set good quality tools to $4000+ for the true enthusiast that can do it all himself.
And then there's the cases, powder, bullets...
$35
