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"GOOD relatively cheap". Oxymoron. You can get "good". You can get "cheap". You will get what you pay for. If there were such a thing as "GOOD relatively cheap"... providing "professional looking footage", the pros would already be using them.

Does "will vary widely in regards to how and where they are filmed" mean "range from nice, bright, controlled lighting to low-light"... and what sort of ambient audio are you thinking?

Which MacBook Pro? Which version iMovie?

Professionals know to work within the limits of their equipment. For example, using a consumer grade camcorder under poor lighting conditions is bad. Add light. Using the built-in mics and expecting audio captured comparable to a $1,000 wireless clip-on mic system is silly.

Used pricing varies too widely. Again, you get what you pay for. Generally, the pros use their gear until it dies, so don't expect much help there. Your budget puts you in the upper end of consumer-grade cams.

Can I re-create your requirements?

1) Large lenses and imaging chip.
2) Mic jack and manual audio control.

The Sony HDR-FX7 will be too bulky (and outside your budget). Canon HF S100 or HF S200 or Sony HDR-CX500 series.
Add a video light (Dot Line or Bescor).
Add a XLR adapter (BeachTek or juicedLink).
Add a couple of mics: Sennheiser or Audio Technica camera mounted base station wireless lavalier and Shure (Audio Technica, Electrovoice, etc.) handheld mic.
Add a tripod and/or Steadicam (Glidecam, Varizoom, etc.) type vest stabilization system.