You won't be able to solve this one quickly, but it's quite easy otherwise. You should gradually build up money without a problem and will want to buy the radar (500) and the extra heart (1000). Just spend 500 more on random supplies as you need/want them. When I ended the game I had at least 2000 gold, and I'd already spent 2000 in the shop to get this achievement, so you shouldn't have any problems eventually getting enough to earn this.