Also, i know how you feel about being just afew points away.
After the arena section on level 12, i had 6700 points, and i needed 7500.
So i bought the 2 upgrades i could, and carried on.
Afterwards i carried on, and died. When i respawned the Multipliers at the bottom had too, so i picked them up, and combo killed the 3 enemies nearby. After crossing the first gap with the ceiling cars, i saw a stack of crates which were hiding a 1000 point style bonus.
So i just managed to get the last upgrade, thankfully.
And i was able to uprgade just after the fat guy burning building section
Would you kindly?