It wasn't because he overspent his pension, exactly, but Harry Truman was the main reason why the President currently is awarded a pension at the end of his service. Truman had no personal fortune, and when he finished his term, he refused to accept any paying positions in the private sector, because he believed that to do so would be to cheapen the office of the Presidency. Unfortunately, this meant that he was left living on the $105/month pension that he earned from his service in the military. This was deeply troubling to many of the Congressmen, Senators, and even President Eisenhower himself, so in the 1950s, a law was passed guaranteeing the former President and his widow a pension, staff support, travel funds, and mailing privileges. This guarantees the former President an income, and ensures that he or she is capable of serving in the ceremonial manner that most presidents take up once they leave office.
The Congressional Research Service has actually produced several very useful documents explaining the history and nuts and bolts of governmental pensions. I particularly recommend Order Code RL34631, "Former Presidents: Pensions, Office Allowances, and Other Federal Benefits" and Order Code RL30631, "Retirement Benefits forMembers of Congress." Both pretty accessible, as far as governmental reports go.
EDIT: To reflect the proper name of the CRS.
Jefferson struggled with finances after his presidency, partially through his own mismanagement, but also partially from a situation that Washington also complained about - visitors. It seems that back in those days, people felt that they could simply show up at an ex-President's house and visit, even perfect strangers. It was expected that the ex-President would house, feed, and entertain these people at their own expense, and that it would be impolite to inquire as to the length of their stay or ask them to leave. Washington (who had no financial issues at all, BTW) complained about how rare it was to spend to spend a quiet simple evening at home with Martha.
So this constant stream of visitors, both old, uninvited friends and new, uninvited strangers, put a serious strain on Jefferson's already struggling finances.
"After retiring from the Presidency, Grant became a partner in a financial firm, which went bankrupt. About that time he learned that he had cancer of the throat. He started writing his recollections to pay off his debts and provide for his family, racing against death to produce a memoir that ultimately earned nearly $450,000. Soon after completing the last page, in 1885, he died."
Arthur St. Clair is probably an answer that meets the spirit of your question, though not the letter. He was the President of the Continental Congress (an office that preceded the establishment of the modern executive branch as we know it) from February 1787 through November of 1787. The President of the CC didn't have the same kind of prestige and influence that the POTUS does, but it was still a prominent and noteworthy office, and St. Clair was a notable figure in his day who at various times also served as the Senior Officer of the United States Army and the Governor of the Northwest Territory. He ended up suffered a dramatic reversal of fortune, however, and was forced to declare bankruptcy, with his home and property ultimately being sold at auction to cover his debts.
St. Clair's fortunes began to wane when he personally led troops into battle against a group of Native Americans led by Little Turtle and Blue Jacket in 1791, and suffered a crushing defeat with substantial losses at the Battle of the Wabash. This cost him his army position, and also a great deal of prestige. He also unwisely made use of personal funds in the administration of the Territory, in the understanding that he would later be reimbursed for this - his later attempts to do so were unsuccessful. St. Clair was a member of the Federalist Party, and when he opposed Ohio's statehood, he got on the wrong side of President Jefferson, who had him removed as Governor. He returned home without power or influence, and his creditors pounced.
After the bankruptcy, St. Clair operated an inn and trading post, and in 1818, he died as a result of head trauma sustained when he fell from the back of a wagon.
This wasn't my main area of focus in history, so I apologize if there were any inaccuracies in my post. I mostly know about him because there's a township south of Pittsburgh named after him, and I did some casual research on its namesake out of idle curiosity.
I don't think there are too many good academic works about St. Clair. There is a decent short summary of his life in a Pittsburgh-area newspaper here, and a longer-form book about him available here.