I'm sorry to say I don't like his conformation at all. I'd think he's worth maybe $100. He's got a weak loin. He's sickle hocked and toed out. His back end is bad. Looks weak. If he was a good weight he'd be prettier but he'd probably not be a horse that I'd want to ride heavily. He probably would be better for kids or a smaller female than a heavier person. He's probably not going to be sound long term as much more than a light trail riding horse.
I'm a smaller female and I don't think I'd want to have a person much heavier than me ride him even if he was a good weight. He looks like he has some nutritional issues too. His tail looks ragged. He may be lazy due to his conformational and nutritional issues.
I think you are right and your mom is not.
The Horse's Ring of Muscles