First off, you'd need to wear a good sunscreen daily to protect your skin, something with full UVA and UVB protection. A bottle of high-protection natural sunscreen like John Masters Organics Natural Mineral Sunscreen SPF 30 will run you about $33, and you'll probably need to replace it every couple of months if you're using it correctly.
Then, you also might want facials and/or peels to keep your skin soft and glowing. A good facial costs about $100 per month, and getting a peel every three months is optimal, so that's another $200 or so. That's $2,198 in preventative products and services per year, or $183 a month on average. For most people, this is more than enough to keep your skin looking superlatively great, and good sunscreen is a necessity regardless.
Total cost: If you're 25 or so now, and the average life expectancy for an American woman is currently 81 (which it is), then you have a solid 56 years of sunblock and peels ahead of you. If you keep up your regimen, over those five decades you'll end up spending around $123,088.
An ounce of prevention is worth a pound of cure, but some people are uncomfortable with the idea of wrinkles, and that's where muscle relaxers like Botox and dermal fillers like Restylane come in.
To keep your face crease-free and full of youthful volume, you could get botulinum injections every three to six months. Botox is between $200-$400 per area, and people usually get Botox in their foreheads and around their eyes.
Restylane is $400–$700, and patients usually have it done under their eyes and in their naso-labial folds. Filler injections have to be maintained every nine months to a year.
Total cost: Assuming you got minimal amounts of both botulinum and fillers (and got them cheaply), that's about $1,600 a year in upkeep for the next 56 years, or $89,600 all told.
Your face isn't the only part of your body that changes with time, though. Significant shifts take place everywhere, especially your breasts, arms, and legs.
Women who worry about their breasts (especially those who've already had an augmentation) often end up getting a breast lift every decade or so, which runs about $5,000–$6,000 per procedure and around $25,000 over a lifetime.
Starting in their fifties, many fans of cosmetic surgery also opt for an arm lift, or brachioplasty, which costs between $5,000–$6,500.
Suctioning out the fat in five "problem" areas usually comes to around $8,000–$10,000, and should last several years. The great likelihood is that the fat will simply start coming back in other areas, and then you can have those lipo'd out too. Over several decades, repeated treatments might total around $30,000 on the low end.
You can get rid of these with sclerotherapy, which involves injecting a vein-busting solution into the offending blood pathways and costs between $200–$500 per session. Several sessions are necessary, and they do re-occur, so maintenance every decade or so is typical. The lifetime sum here could easily reach $4,500, if not more.
Total cost: Keeping your body in stasis year after year would have a price tag of around $66,000.
A standard facelift can range anywhere from $7,000–$10,000 with hospital stay and aftercare.
Eyelid tucks, cheek implants, and other facial detail procedures set their recipients back around $4,000–$5,000 per surgery.
Total cost: You might wind up paying about $12,000 if you're parsimonious and only want one facelift and one more minor surgery.
Not including other add-ons like teeth whitening, cellulite treatments, or body skin care, a lifetime of continuing to look as close to 25 as modern medical science allows will leave you with a $290,088 tab. Or you could, you know, buy a place to live instead.