I would encourage you to take your time looking at the market in your area and viewing lots of units online. PPL website is great for this. They always have a floorplan although they have few $10,000 units.
I would not take $10,000 for ours and it is almost 13 years old. Most that I see in my area are only less than $10,000 if they are 70's to 80's. That is an old machine due for lots of trouble.
If you have a fund for repairs, I suggest you increase your baseline price to at least $15,000. We didn't even put tires on ours for the first year we owned it. So our expenses were spread out a bit.
From what I have read, I don't get much better mileage than the longer units. We say 9 on a good day. I also have a scangauge and I love it. They say if you watch it and try to keep your current mpg higher than your average, you will get the best mileage. But as others say, we hardly worry about mileage at all since we are out to have fun. After you pay your airfare, do you worry about that cost the whole trip?
I must stay that RV'ing is a great activity for retirement. We also bought ours a few years before and had fun learning its ins and outs and doing some repairs, some that were the result of our learning curve!
Good luck.