The write cycle life can be as low as 500 writes. It depends on the type of memory being used. I don't know where people get 100,000 from - unless there have been major advances since the white paper below. Budget cards may not even have wear leveling.
From a white paper by Kingston (see emphasized section below for most relevant data):
• Solid State: Flash storage devices, as semiconductor storage devices, have no moving parts and thereby are not
subject to the mechanical failure issues of hard drives. Their overall data reliability enabled them to dominate the
convenience-oriented portable memory products market, operating silently with a zero decibel noise level.
• Small Physical Size (or Form Factor): Flash storage devices are designed to be easily transported. Convenience is
an important criterion, especially for consumer and corporate applications.
• High Data Reliability: Flash memory is very reliable and many of the Flash storage device types also include Error
Correction Code (ECC) checking and advanced wear leveling.
For example, Kingston’s solid-state drives have a rated error specification of less than one (1) bit in 1,000,000,000,000,000
bits read (1 bit per 10 15 bits read).
• Kingston Flash Data Retention: Kingston Flash Storage Devices primarily use MLC/TLC Flash Memory. Data
retention on Flash memory is dynamic since the amount of time the memory has been cycled affects data
retention. Important information should always be backed up on other media for long-term safekeeping.
• Wear-Leveling Technology: Kingston Flash storage devices incorporate controllers utilizing advanced wear-
leveling technology, which distributes the number of P/E cycles (program/erase) across the Flash memory evenly.
Wear-leveling thus extends the useful life of a Flash memory card (for details, please see Kingston Flash Cell
Endurance section, next).
• Flash Cell Endurance: Non-Volatile Flash Memory cells have a finite number of program/erase (p/e) cycles. Simply
put, every time data is written to or erased from a Flash Storage Device the number of program/erase cycles
decrease and are eventually used up to the point that the Flash memory is no longer usable.
• For Multi-Level Cell (MLC) Flash, up to 3000 write cycles per physical sector based on current lithography process (19nm and 20nm) at the time of this writing. For Single-Level Cell (SLC) Flash, up to 30,000 write cycles per physical sector. For Triple-level Cell (TLC), up to 500 write cycles per physical sector. Lithography of the Flash Memory Die plays a key role in cell endurance and decreases as the size of the die gets smaller.
• Flash Memory Technology: For Multi-Level Cell (MLC) Flash use multiple levels per cell which will allow more bits
to be stored using the same number of transistors. MLC NAND flash technology uses four possible states per cell.
As for Single-Level Cell (SLC) each cell can be stored in two states. For Triple-Level Cell ( TLC) the bits are allowed
to be stored in eight possible state. Lithography of the Flash Memory Die plays a key role in cell endurance and
decreases as the size of the die get smaller.
• Write Amplification Factor: Write Amplification Factor or “WAF” is present in all Flash Storage Devices. The write
amplification factor is the ratio between the amount of data written from the host and the amount of actually
data written to the Flash memory chips. All Flash devices write in full blocks, which means, that in order to write to
a block that may already contain some data the Flash controller must move the existing data in the block (usually
to memory) and combine it with the new data and write all the data back to the Flash memory. For example a
2MB file could be written by the host to the Flash device however 4MB of total data may be written to the Flash
memory to complete the write operation. In this case you would have a write amplification factor of 2. In some
cases the WAF can be as high as 20 or 30.
• Automatic Bad Sector Remapping: Kingston Flash controllers automatically lock out sections with bad memory
cells (“bad blocks”) and move the data to other sections (“space blocks”) to avoid data corruption. During factory
formatting (as described in Section 2), spare blocks are set aside on the Flash storage device for remapping bad
sectors over time to extend the useful life and reliability of the Flash storage device.
https://media.kingston.com/pdfs/MKF_283.1_Flash_Memory_Guide_EN.pdf
This "Test to destruction" article regarding SSDs will be of interest since SSD use the same memory:
The SSD Endurance Experiment: They're all dead - The Tech Report