I was around the 200,000 point mark before finishing the remaining achievements on Jetpac. So my recommendation would save this one for last before grinding this one out.
To grind out the remaining 50,000 points or so that I needed, I continued playing until I was up against the bird/plane enemies that linger on the edges of the screen. Due to their attack pattern they usually spawn close to one another and often kill themselves against the platforms, giving you free points. Once there, I fueled up my rocket (so that bonuses would spawn more frequently) and sat between the left and middle platform while casually gliding up and down and shooting my blaster as enemies spawned (see image). Picking up bonuses also speeds this up.
Enemies range from 50-60 points.
Bonuses are worth 250 points.
Acquiring a fuel canister is worth 100 points.
I was picking up around 6,500 points every minute with this method, so if you fall in a similar range, you can expect to finish this achievement up in roughly 8 minutes. When the achievement unlocked for me, I was at 253,000 so give it an extra minute or so as it may unlock on a slight delay.