I would definitely consider a lease instead of ownership. I know it varies upon location, but where I am $200 is extremely low, even for self board. Full on self board at my barn I believe is ~$350, give or take. Also depends on facilities and what is included in that board price.
I own two horses and have them both on semi-self board and pay just about $900 on board alone each month. I had them both on full board at one point and was paying around $1200 per month just in board fees. I have yet to hear of a decent farrier in the area who charges anything less than $100 for trim/all fours. I pay $170 every 5 ish weeks ($135 for my mare who has all fours, and $35 for my pony who is barefoot). And this farrier is GOOD but very reasonable costs for the job she does and considering the area we live in. I spend anywhere from $50-$300 per month extra for supplements, just depends on the time of year, etc. I do my own vaccinations so that averages me maybe $200 or so per year. I have my vet out a couple times per year for checkups/teeth floating. Her call out fee is $90 for non emergencies and I believe $120 for emergencies. Depending what I am having done I spend anywhere from $300-800 per visit on that. I generally average 1 emergency per year (knock on wood ...) so obviously that costs much much more than my average visits.
On my "cheap" months I spend around $1100 total on both mares.
On an expensive month (not including an emergency) I have spent as much as $2200. And I'm not including any "extras" such as blankets or new tack if/when it's needed.
Sorry for such a long post, but thought I may as well back up my reasoning for WHY $300 seems too low IMHO. Not trying to sound harsh by any means, only realistic.