Agreed. If your income is high enough to save $100k/yr, it's high enough (assuming good credit) to qualify for an excellent rate on 15-yr fixed loans (or 30yr but you get a better deal on 15yr and it saves you tens of thousands if not more over the life of the loan). By "qualify" I mean meet the bank's required debt-to-income ratio; the interest rate, of course, depends on your credit.
Assuming you're not planning to live there, you will need 25% down and about another 5-10% in closing costs etc. for each house, so with the $100k, in your area you could buy THREE houses each year instead of one. Even if you are planning to live there the bank may require a substantial down payment, much more than the baseline 3%-5% FHA amount, if you're buying a multi-unit to be a partial investment property... we needed 15% down on the 3-unit we live in.
Since you're in an area where decent houses can be had for $100k, you would be looking at something in the neighborhood of $750-$1000/mo per house on a 15-yr fixed loan, depending on property taxes in your area and on how good your credit is (i.e. what interest rate you can get). If you can get them for less than $1000 and rent them for $1000, then you have three houses per year for which someone else is paying your mortgage (i.e., buying you a house) and also giving you a few hundred bucks a month to help cover your expenses (maintenance etc.). One of the KEYS here is to get fixed-rate mortgages, because then apart from occasional possible property tax increases, the mortgage stays the same but the rent goes up every other year or every year.
Then in 15 years, you start getting rid of the mortgages--starting 15 years from now, every year three of your houses will stop having mortgages! Making all the rent, minus property taxes/maintenance, yours... and unless you buy in an area that's going downhill, the rent will have gone up pretty significantly. This to me sounds like an excellent retirement plan. It's what my husband and I have done, except that we aren't going to be able to buy three houses a year anytime soon (in the past year and a half we bought three properties totaling six units, of which we live in one, and that's it for a while until a new cash influx occurs).
One thing to consider is what you can do to maximize the rent. Like, would an extra $3000-$5000 investment up front to spiff up the bathroom and/or kitchen, or refinish the wood floors, or whatever, enable you to attract higher-paying tenants? Also, once you find good tenants, don't gouge them--our policy with good tenants is to keep the rent the same in year 2 and only raise it in year 3, because if you raise it every year you increase the chance of losing good tenants and going a month or more with nobody there.