Though your wife is a political refugee, she is not on "refugee" status as far as USCIS is concerned. She is a "parolee", intending to adjust status on the basis of marriage to a USC. As such, she is not exempt from the public charge grounds of inadmissibility, so not eligible for I-485 fee waiver. More info here -- https://www.uscis.gov/policy-manual/volume-8-part-g-chapter-3
Note that you only need to pay the I-485 filing fee (currently $1,140 + $85 biometrics fee = $1,225 total). There's no fee for submitting the I-864 with the I-485. Filing I-765 and I-131 are also (still) free, if filed along with a full-fee I-485.
As for the medical, you may be able to get discounts at a clinic that caters to refugees and asylees. Check the thread below for @Adventine's experience, to get tips on finding a similar clinic in your area --