Mechanical Turk allows creating microtask assingments on the web.

The most robust way of doing it is by using an external question and posting the tasks through the API.

<?xml version="1.0"?>
<ExternalQuestion xmlns="http://mechanicalturk.amazonaws.com/...">
    <ExternalURL>https://example.com/turk</ExternalURL>
    <FrameHeight>620</FrameHeight>
</ExternalQuestion>

Price is the assingment reward and +20% for Amazon. When posting a task with 10 or more assignments, you have to pay 20% extra, but you can circle around that by creating multiple HITs with 9 assignments each. Only minus is that a single worker can do th same HIT multiple times, which might be an issue in some tasks.

Reward pricing depends on:

• wanted result quality, but you must then add qualifications
• assignment time, more time it takes, more you should be paying
• how fast you want the results, paying above the median award

US minimum rate:        $7.25    / h
Median turk in 2010     $1.38    / h
High-end workers        $8 - $14 / h

Sources

• The Myth of Low Cost, High Quality on Amazon's Mechanical Turk