While ADA rules may not apply, keep in mind that long and/or steep ramps or excessively long ramps without level resting platforms are very difficult for a person in a manual chair to navigate, even with the help of a caregiver. For some disabilities the 1:12 pitch can seem insurmountable. Adding on turning or resting platforms and switchbacks can really add to the cost. The fact that ramps usually must be built outside does not help either. Throw in a little steeper pitch and some inclement weather and it gets dangerous for both pedestrians and chairs. Even power chairs will have problems with weather and steeper pitches.
I was able to find a 72" porch lift on ebay, won it for $1250 and drove 12 hours round trip to bring it home. It was only 6 months old and the guy had paid over $9000 for it to be installed just a few months earlier. The family said he used it twice, went to the hospital and never came home. For them it was a constant reminder and they wanted it gone. For a long term need I would not consider any other way to get in and out. It took a while to find but worth it in the long run. I cut a door in my garage especially for the lift. It lifts my son 55" from the garage floor directly into his bedroom. He can ride the lift in comfort, warm and dry, something a ramp does not offer. He will need it for the rest of his life, so doing it right was imperative. This has been in use for 10 years now and it definitely was the way to go.
For a short term need, renting a modular ramp might be cheaper, but my bet is that will get expensive fast too. Building a good ramp is neither cheap or easy and cost escalates pretty fast. Buy a lift and resell it when you no longer need it. If you can find a used one you probably would not lose much on the deal.