Daily driver small block build

I am hoping to eventually have a warmed over small block in my daily driver 69 dart. This is not something I am in any rush to get done: I'd like to start collecting parts soon so I can have everything ready by next summer. Just trying to get advice on a starting point. Some main goals:
- Spending less than a few grand total
- 300 HP
- Solidly double digit gas mileage
- Solid low end torque
- Runs on 89 octane

Some questions:
- 318s are a dime a dozen where I live. $300 for complete motors left and right. 360s are a bit harder to find and a little bit more expensive, but would it be worth it to find one?
- Is a roller camshaft worth it at this level?
- Which heads should I look for?
- Compression ratio?