I've never used the Keystone A-7. However, before I can offer
any advice at all I think it would be good to know just a little
more info. When you ask, "Is this a good camera to start with?"
what do you mean? Since the Keystone is a spring wound camera
you cannot use it for sync sound. It's tiny lens is very limited and
there are very few controls. It was a "point and shoot" camera
so you will learn nothing about exposure, focus or aperture settings.

When you ask to be pointed in the direction of a good beginners
camera that is budget friendly what do you mean? Are you looking
in the $60 range? Can you go higher? Are you looking for a beginners
camera that uses different lenses? One that will allow you to adjust
exposure and aperture? One that will allow you to also record audio
- meaning a crystal sync camera? without knowing anything I'll just
stab into the dark and list some 16mm cameras for you to take a look
at.

Bell & Howell - old cameras, usually spring wound. Good
solid cameras to start with and very inexpensive.

Krasnogorsk a Russian made camera that many first timers
use. It takes 100 daylight spools - about two and a half minutes.
It runs loud so that makes it difficult when recording sound and
that 100' spool makes for short takes and lots of reloading.

Bolex - the great workhorse of 16mm. Many different models
to choose from. The "H-16" is the first 16mm camera I bought and
I still use it. You can usually find them for not much money.

Beaulieu - the "R16" is one of my favorites. They are great
cameras with a beautiful lens and used are very inexpensive. Its
a little loud, but can be quited with a barney.

Eclair - the NPR is the camera many film schools use. Rugged,
solid and quiet.

Canon - the Scoopic was the standard in TV news cameras
in the 1970's. Easy to use. Another film school staple. Before video,
every film student used the reliable Scoopic before moving up to the
Eclair.

CP-16 - a really nice, solid camera with crystal sync and most
come with an excellent Angenieuz zoom lens. These were used for
news gathering for decades.

With the Aaton and Arriflex we're getting pricey. These
are high end, pro cameras worth knowing about. These are usually
rentals - even used they can run above $10,000 - but it's worth
knowing about them.

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The aim of an argument or discussion should not be victory, but progress.
Joseph Joubert, essayist (1754-1824)