Cost of amputating a leg? At least $20,000. Cost of an artificial leg? More than $50,000 for the most high-tech models. Cost of an amputee’s rehab? Often tens of thousands of dollars more.

These are just a fraction of the medical expenses victims of the Boston Marathon bombing will face.

The mammoth price tag is probably not what patients are focusing on as they begin the long healing process. But friends and strangers are already setting up fundraisers and online crowd-funding sites, and a huge Boston city fund has already collected more than $23 million in individual and corporate donations.

No one knows yet if those donations — plus health insurance, hospital charity funds and other sources — will be enough to cover the bills. Few will even hazard a guess as to what the total medical bill will be for a tragedy that killed three people and wounded more than 270. At least 15 people lost limbs, and other wounds include head injuries and tissue torn apart by shrapnel.

Bombings survivor Heather Abbott said Thursday she has already gotten offers of help to pay for an artificial leg. The 38-year-old Newport, R.I., woman was waiting in line to get into a crowded bar when the bombs went off.

“I felt like my foot was on fire. I knew I couldn’t stand up,” she recalled from her hospital bed. Surgeons amputated her left leg below the knee.

Health insurance, as practically anyone who has ever gotten hurt or sick knows, does not always cover all costs. In the case of artificial limbs, for example, some insurance companies pay for a basic model but not a computerized one with sophisticated, lifelike joints.

Rose Bissonnette, founder of the New England Amputee Association, said that the moment she heard about the bombings, she knew immediately that her organization’s services would be needed. The advocacy group helps amputees navigate issues such as insurance coverage for artificial limbs.

Bissonnette shared one group member’s struggle to get coverage for artificial arms as an example of the red tape some bombing victims could face. The woman “got a call from the insurance company and the person on the other end said, ‘How long are you going to need the prosthetic hands?’ ” Bissonnette recalled.

Health economist Ted Miller noted that treating just one traumatic brain injury can cost millions of dollars, and at least one survivor has that kind of injury. He also pointed out that the medical costs will include treating anxiety and post-traumatic stress — “an issue for a whole lot more people than just people who suffered physical injuries,” he said.

Many survivors live in Massachusetts, a state that requires residents to have health insurance, “which should cover most of their required treatment,” said Amie Breton, spokeswoman for Massachusetts’ consumer affairs office.

Amputees may face the steepest costs, and artificial legs are the costliest. They range from about $7,200 for a basic below-the-knee model to as much as $90,000 for a high-tech microprocessor-controlled full leg, said Dr. Terrence Sheehan, chief medical officer for Adventist Rehabilitation Hospital in Rockville, Md., and medical director of the Amputee Coalition, a national advocacy group.

Legs need to be replaced every few years, or more often for very active users or those who gain or lose weight. Limb sockets need to be replaced even more often and also cost thousands of dollars each, Sheehan said.

Massachusetts is among about 20 states that require health insurers to pay for prosthetic limbs, but many plans don’t cover 100 percent of those costs, Sheehan said.

Some insurers may be willing to make exceptions for the Boston blast survivors.

“We will work to ensure that financial issues/hardship will not pose a barrier to the care that affected members’ need,” said Sharon Torgerson, spokeswoman for Blue Cross and Blue Shield of Massachusetts, one of the state’s largest health insurers.