If the upfront $129 fee is too high, consider starting at $9/month per user (billed annually). This gives you the same wireframing tools in a browser, plus real-time collaboration. You can subscribe for one month, finish your project, and cancel. That is far cheaper than buying a perpetual desktop license for a single use.
Balsamiq offers a of the desktop app with no feature restrictions. You can save, export, and create as many wireframes as you like. For short-term projects or evaluation, this is the perfect solution. No crack, no risk. balsamiq wireframes license key