Just came across this deal on aliexpress, not sure how good they are, the brand is a reasonable one. Not as high output as Gooloo models posted here but will do the job for some.
Some specs from listing:
Capacity: 8A/h/3.7V/29.6Wh
USB input 5V/2.1A
USB output 5V/2.4A
Start-up current 400A
Peak current 800A
Suitable vehicles:petrol engines less than 4.0L or diesel less than 2.5L
Not sure why the price was changed in the title, for me it comes up as US $40.87 / AU $57.84