RF Explorer is a "budget" option at around $300-400: http://rfexplorer.com/models/

Professional handheld spectrum analyzers are in the $3k-50k range from the likes of Keysight, Anritsu, etc.

Many vendors will also rent out them by the day. There used to be a company in Denver that did back in my WISP days.

Plug a cheap SDR dongle into your laptop and install some free software SDR app.

http://www.rtl-sdr.com/

It might seem like the poor man's approach, but plug a good Yagi antenna into that dongle and it becomes quite powerful.

rtl_power frequency hops at about 80 MHz/s max. You can use https://github.com/xmikos/qspectrumanalyzer or many other rtl_power frontends to see it in real time as you point the antenna. For windows there's https://github.com/pavels/spektrum

Another approach seen on hackernews in the past had an omnidirectional antenna and used GPS tagging to make heatplots at different frequencies overlayed on a map. ref: http://www.tautology2.net/heatmap/ It uses the http://eartoearoak.com/software/rtlsdr-scanner software.

with an android phone and a usb-otg cable, you can plug the rtl-sdr directly into your phone and use an app to view/listen to the spectrum

The rtl-sdr dongle I have (ATS-B receiver) draws too much current to be used with my tablet (Nexus 7 2013). At minimum, a powered USB hub would be required in this setup for it to work properly.

I have a RTL2832U/R820T reciever ( https://www.amazon.com/NooElec-NESDR-Mini-Compatible-Package...) (note - there are newer models now) and it works fine with a samsung galaxy note 3.

http://sdrtouch.com/

Spectrum analyzer and appropriate antenna.