That's pretty risky - you'd need to put 25K into one company to make it worthwhile for the company. Angel investing is like VC on crack; you have to spread your investments around because the failure rate is likely going to be well over 50%. The goal is to make the 1 or 2 in 10 that succeed pay off well enough to obviate the cost of the failures.
You really don't need a lot of money to invest. Just look at the HN model. As an angel all you need is 25K to get into most early rounds.