Well, you could try the dual ips system from gws. There's a 5.9:1 and a 7:1 gearbox for these, with 5-10 oz of thrust, depending on how you prop it, on the 5.9 and from 8-10 on the 7. Both setups on that one will draw about 2-4 amps. The 300c with type d kicks out from 7-12 oz of thrust, while drawing as high as 8.5 amps. Now, with retiming, you can get these numbers up alot higher, and the amp current draw will also go up. So while the dual ips system may not be quite as powerful, it draws alot less current, so longer flight times. The problem is getting it to put out the thrust like the 300c.

Other option is to get something like an acro 280. Only problem is the motor alone is $40.50. Add on a decent gear box, you're looking around at around $56... a bit higher then you were looking. Also the graupner speed 330 @ $29.90. Puts out about 15 oz of thrust with a 2.3:1 gearbox, so I can imagine if you put a higher ratio on it you can get more out of it, espically if you retime it. Hope this helps!