There's no way to estimate an average yield... so much depends on many different factors...
Tips for growing autoflowers, though -
1. Don't give them any nutes for the first week or two. When you DO introduce them, do so at 1/4-1/2 strength. You can increase the next week if they tolerate them well... but I've never met an autoflower (and they're all I grow) that can withstand full strength... and all feed charts are written for photoperiods, not autoflowers.
2. Don't do any high stress techniques on them - they don't like it. Stick to LST but LST is very worthwhile as you will increase your yield.
3. Look for signs of pre-flower around Week 3 or 4 and start cutting back your grow nutes and adding in bloom nutes.
4. Always pH everything you give them... water/nute solution. pH levels should be between 6.0 and 6.5 during veg and 6.0 to 6.2 in flower.
5. Enjoy the hell out of what you're doing... it's a fun and challenging ride!
Good luck!