What's a 550SH motor? Is it a 280?

I think you should spring for the speed control.

The battery pack you showed is for RC Cars. Probably doesn't matter but I thought it interesting. Keep in mind that a 30 minute charger means you have to twiddle your thumbs for 30 minutes. Also, the one shown looks like it uses AC, so you can't use it at the field.

Finally, any time they say you can use EITHER a six or a seven cell pack that probably means with six it will (eventually) take off and that you really need a seven cell pack.

Budgetting is fine, just make sure you don't end up spending more because you skimped the first time.