Average Salary: $60,370
Expected Lifetime Earnings: $2,336,000
The federal pay grade charts make the salary portion fairly cut-and-dried, here. Government employees make money based on the General Schedule. The GS is a series of ascending pay grades, with a sweet step-by-step pay increase within each pay grade. Think of it as leveling up, except instead of experience points, you get cold hard cash.
You'll probably be hired at a GS-7 level, which is good for $40,000 or so per year (source), and you'll get minor pay increases within that as you build your reputation. Getting up to GS-9 will get you closer to $50,000, as well as better benefits. There's a level cap in the agency of GS-13, at around $70,000, so you can pretty much look at that number as the ceiling.
There's also the added bonus known as locality pay. It sounds really boring, but what it means is anything but that. Wherever you live, it costs money to live there. Rent, groceries, and dozens of little living expenses that can really add up.
The government recognizes this and will give you cash to compensate for the relative costs of your expenses in the place they're making you live. In a place like Chicago, that translates to an extra twenty-five percent, just because Chitown's kind of expensive.
If you speak a foreign language, you might be able to snag even more for your checking account. This one-time bonus, a whopping quarter of your basic yearly pay, will be paid to those who can prove they're generally proficient in another language (source).
For the record, generally proficient means you should have enough vocabulary and structural knowledge to easily carry on informal and formal conversations on just about any common topic, including professional subjects. You'll get the lump-sum bonus when you graduate from the Secret Service's training academy.
No word on whether they give it to you in a massive treasure chest. But one can hope, right?