Obviously costs vary wildy by location. I can see by some of the posts, there are people that are very lucky...
My horses are in a commercial barn. Typical cost for my area (at a facility) are:
The above, along with mucking of stalls are included in "full board" which runs anywhere from $750 to $1200 per month. If you want to go to a fancy show barn, monthly cost can be $1,500 to $2,500 or more.
Shoes: $125-$175 standard. More for special shoes. $60-$75 for trimming only.
Vet: My horses don't get sick. :) That said, at least ONE thing happens each year that warrant a vet barn call. Barn call is $200 plus treatment/meds. By the time we are done, I seem to always have at least one vet bill per year that costs from $600-$1000.
Fall and spring shots typically run about $40-$50 each. The vet does several horses at my barn so there is no barn call fee over that.
Tack: Depends on your taste and budget. You can by a saddle, bridle, etc. for under $1000. Take good care of it and it can last you a while. You can also spend $5000 on a saddle.
If you have the budget, I would put down $2,000 for one set of tack and some basic grooming supplies to start. Not the "best" but good quality. After year one, you can budget from $100 per year to whatever you are willing to spend.
Insurance: Depends on level on insurance and horse value. Mortality and major medical for a <$10,000 horse (not a fancy show horse) should run about $500 per year.
Liability insurance should also be considered, especially if you are keeping horses on your property. A homeowners policy may or may not protect you here. Check with your agent and get it in writing. If you need additional coverage, it should only run a few hundred a year.
Trailer: You can get a used trailer for about $1,000. You can buy a trailer with living quarters for $60,000 to over $100,000. Depends on budget. If you are looking to save money and stay relatively local, you can find a very good used 2h bumper pull for $2,000. Again, depends on area.
Don't forget you also need a vehicle to pull the trailer. Learn about GVW, GCVW and the TRUE towing capacity of your vehicle. I also feel you should NOT pull a horse trailer with a car, jeep or small SUV. Horse trailers have a higher center of gravity than campers or equipment trailers. Something like a Suburban or F-150 will do the job - just make sure it has the right options to tow a horse trailer.
Blankets/Sheets: Included in the tack figure above. I believe blankets are a luxury not a necessity in most places. Either way, you can get a decent blanket for under $100 and it should last for years.
In my area, the total would be:
$750 (low end) full board/month = $9,000/year
Trimming (barefoot) = $65 x 10 (every 5 weeks) = $650/year
Fall and Spring shots @ $50 each = $100/year
Inevitable vet bill = $800/year
Total = $10,550 which sounds about right.
I also travel to shows and competitions with my own trailer. I do about 8-10/year. Each one involved about $200 in tolls and gas and an average of $100 in entry fees. Two or three involve an overnight stay - two nights at $150 each, plus stabling the horse at about $25/night.
So my "show" costs are about another $4,000.
Now you made me sorry that I added all that up. I kind of knew, but it is scary to think I spend about $15,000 (much more with tack and other purchases) per year on this hobby. I should have stuck with jogging or joined a health club. :)