TL;DR: I bought a Roomba I3 for $30. Turned it into an I3+ for less than <$100. I feel like I won and just want to brag about it.
Long story short: My old Roomba was old (700 series)...My regular vacuum broke...Something spurred me to look on craigslist for a cheap new vacuum. Found a Roomba I3 posted for $30. I was skeptical, but I know that Roombas are fairly easy to repair. I found warnings about a subscription program and certain Roombas being bricked...but the I3 wasn't part of the program.
I found the person and bought the Roomba. Her reasoning for selling it was that she wanted a Roomba that auto-deposits (she had the base model, and didn't realize that the I3 already does it). She spent upwards of $1k for a new Roomba. She was also complaining about how it just doesn't work as well as it used to.
I took the Roomba apart and cleaned it, inside and out. There was just a bunch of hair. Ordered replacement brushes and filters. Its works so freaking well. It cleans my floor better than my older model ever did.
So I didn't waste $30; so I decided to just go find the pieces I needed to make this model auto-deposit. I bought a clean base on craigslist for $65, and the guy who sold it to me also threw in brand new filters, new brushes, an extended life battery, and a regular battery, and some of the vacuum bags for free. Win.
I found an auto-deposit dust bin on ebay for $17. Win.
I feel like I won and just want to brag about it.