Help William Repair His Lifeline Vehicle

Hello my name is William Matthews I'm disabled and currently on SSI I recently had my transmission go out on my vehicle I'm taking care of two elderly family members 73 and 79 and I really need a vehicle money is extremely tight since I'm living on a limited income so anything that I could get put towards this repair would be extremely helpful I have a lead on a transmission for $885 shipping $178 and I might have a mechanic that could help me I'm not sure what he's going to charge me most people charge an hourly rate at like $150 an hour in my area so I was thinking probably $1,000 to $1,200 to install the used transmission there is a transmission that is new from the same person that is $1,600 that would be amazing I'm not a greedy person so I'm settling for the used one it has 98k miles on it the used one I'm basically a foot being disabled and trying to take care of two elderly parents anything will help thank you