Koolertron's GH-CJDS66-FU is a dual-channel DDS arbitrary waveform generator with a 2.4-inch display, listed at $169.99. Sine output runs to 60 MHz, square and triangle to 15 MHz, and pulse and arbitrary waveforms to 6 MHz. Far more relevant to plate work is the low end: fine steps, 1 mV amplitude resolution, adjustable duty cycle, and a long list of built-in waveforms plus 60 user-defined slots.
The second channel is the reason to buy this rather than a phone app. Feeding channel one to the driver and channel two to a strobe or LED gate, with a controllable phase relationship, is how you freeze a Faraday wave or walk a pattern slowly rather than watching it blur.
The same board is sold under several brand names, so shop on specification and price rather than on the logo.