I see in your profile that you're 23 years old. I'm 53 myself. If I had bought the kit 30 years ago I'd have saved much more than $300 on repairs and the one-off tools I've bought. The question you need to ask yourself is this: Will I be doing more than adjusting cables, swapping chains and tightening parts? Will I be disassembling and assembling bikes?
The last frame I bought had an integrated headset, and I had the shop installl the mega-exo BB. Everything else I did myself, but I didn't need any special tools, mostly just allen wrenches and a chain tool. $300 is a lot for allen wrenches.