1) Set up a budget for approval. Any expenditure which has already been approved at the previous annual meeting need not be brought up again for specific approval. If you budget $2000 for church van maintenance and repair, and its transmission needs a $1000 overhaul, then go ahead and get it repaired.
2) Each board or church department should make a good faith effort to stay within its budget. But if a budget item is exceeded through ordinary but unexpected situations, then
- report it at the next business meeting;
- b) explain why;
- c) move on--i.e., don't worry about passing a budget increase;
- d) increase your budget for that particular item next year.
- The more unusual the item is, the greater the need to bring it to the congregation
- The more expensive the item is, the greater the need to bring it to the congregation
- The more time-sensitive the purchase is, the greater the need for the board to deal with it outside of congregational oversight
- Sometimes difficult situations of a most sensitive nature need to be dealt with in the privacy of the board meeting, for example, a severance package for a dismissed ministerial professional. In which case, the board members stick their neck out and assume that the congregation will trust their judgment. After all, the board members are the supposed to be the most spiritual mature and Spirit-led members of the congregation. Moreover, the board members should carry enough voting weight as to control any future votes on the controversial issue.
All this to say, there must be some flexibility. The principles of congregational governance need to work together with the principles of board representation. The board members function for the purpose of facilitating church governance and should not compete against it.
Ultimately, instead of asking if you should make a rule that congregational approval is necessary for purchases over $500 (or over $5000...), you should leave the exact figure undecided, and allow for prudence according to the situation. You could use some less than precise language to convey this. "If an out-of-budget expenditure of pressing urgency cannot be brought before the congregation in an expedient manner, the board, if the nature of the circumstances deems it necessary, may authorize reasonable disbursements of limited amounts without prior consent of the congregation."
But sometimes things are better left unsaid.