I work as a heavy equipment operator for a sewer and water main company in downtown Toronto, but I have the ambition to do more than just work for someone else every day. 

Then add that due to your having issues with almost running over tie outs and your equipment soiled by dog feces in the yard, you will have to insist that the no pets clause be complied with and any future sign of any animal will be a violation of the lease.  

Couple that with the resilience of the local job market, and DC would be better equipped to weather even a hypothetical bubble burst than many other major cities.

Figure out either an internet business(either dropshipping, ebaying, affiliate marketing, content creation(writing, reviews, videos, etc)(dude, start a blog now, put content on it, you put your story here, you can put it on your blog and eventually it will rank, even more as you progress your life improvement strategies))    ------    or start a super low overhead service business to start and run(think mobile/stationary car wash&detailing, cleaning service, maybe high demand time uber driving etc), or one possibly related somehow to real estate (if that is your interest)- like Landscaping(not maintenance-due to high equipment costs).

But you need to open the equipment door behind the coin box to access that mode. 

Expect it to be done on day 30"You say "Forget it I want to cancel then"They say "OK but I'm keeping the $50"You say "Whoa never mind I'll still get it, should be out in the next day or two anyway"They say "Tough we are keeping it and we refuse to give you service"They may be within their rights and they did have people on the phone dealing with you and had to schedule around your proposed time and may have ordered some equipment that is sitting in a warehouse, advertising costs to get a new subscriber etc.

The seller said that she already got an offer to rent it 800/month from a local handyman in order for him to store his equipment but she's more keen on selling.Any idea how I should approach coming to a price and negotiating for this thing?

The more you learn the better equipped you will be to find and solve the problems that can put projects out of reach for most folks. 

Many companies who build equipment have to prove they are ISO 9001 compliant to sell to some of their customers.

Providing equipment is an implicit understanding that they can use it safely.