Things to consider. How wide are your stairs? Will anyone else need to use them? Are there any other options? Will the lift be able to be fitted so that you can get on and off the seat? I know this sounds silly but if you have mobility issues and/or are short, this may be a real problem. Will you be able to afford the servicing and repairs? I wouldn't go for used, maybe a recon with warranty from a good supplier. Usual advice, get three quotes, DON'T sign anything when they visit, get all three quotes and have a good think. Have someone with you when they visit.