This kind of thing is usually workable.
These units, which are available for around $50 in a less expensive version, typically have a 7 Amp Hour Sealed Lead Acid battery.
Don't let the "7 Amp" fool you. That's capacity, not current flow. They will put out 50 to 60 Amps for a brief period, enough to start most cars most of the time.
They are available on eBay and elsewhere relatively inexpensively. I carried one all the time until I put an auxilliary battery in the van which I can override to start the thing if I have to.
Arf