It may depend on where you are at. Last week, we were given a mustang pony. He's 14, in good health, was born wild in the desert, used for a kid to barrel race, spent time on a ranch working cattle, and been a lesson horse. He can carry me at a gallop comfortably, and after his first "I'm really nervous' ride here, is proving easy to stop, slow, turn, change pace, etc. He's been available for 5 months "free to a good home".
Last December, I sold a purebred Arabian mare, outstanding temperament, comfortable with her paces but still green, but absolutely willing - and sold her for $600.
A charity sent out 9 (IIRC) horses needing adoption to professional trainers for 2 months of training, followed by a public 'competition' to show off what they had accomplished with them. 2 of the 9 have been sold for the adoption fee - I think around $1000. The other 7 are still available.
Around here (s. AZ), it would be tough to add enough value in 30-60 days to cover your feeding expense for that time.
The mare I bought for $800 and sold two years later for $600, ridden by my then 12 year old daughter for one of my daughter's first lessons: