THERE’S nothing New Yorkers love more than a bargain – whether it’s tax-free shopping or cut-rate meals during Restaurant Week.

So it’s little wonder that the first annual Spa Week, which offers “every service for $50,” is selling out fast.

“We know so many people who lead very stressful and hectic lives,” says p.r. exec Cheryl Reid, co-creator of the event.

“People just cannot afford to take care of themselves – and we wanted to make spas affordable.”

From Monday through next Sunday, 33 spas in Manhattan and Brooklyn are letting consumers sample their pricey treatments at just $50 each.

Many services are already sold out, but (at press time) you can still book a one-hour massage at Downtime spa in Park Slope (115 N. Seventh St., [718] 218-9680), a foot-reflexology session at Azure (227 W. 29th St., [212] 563-5365) or a more elaborate-sounding Integral DNA Facial at Atzen (856 Lexington Ave., [212] 517-2400).

Of course, there’s a bit more to the event than the altruistic idea of bringing the lux life to the masses.

“It’s a very competitive industry,” says Mary Blackmon DeRoker, the event’s other co-creator. “The day spa is one of the fastest-growing segments in the spa industry.”

And what better way to drum up new customers than to get them hooked on the pleasures of a weekly, hour-long shiatsu session, a scrumptious hot-chocolate body treatment or a decadent hot-stone massage – which is one of the best deals going during Spa Week, says Reid.

“That’s one of the most expensive massages you can have – it can run from $125 to $145.”

Just remember: Your tip should reflect the full price of the service, not the discount. But it’s still a small price to pay for de-stressing in style.

For more information and a list of participating spas, go to spa-addicts.com/spaweek/fulllist.asp.