Spring Is Approaching: The high school prom can be a blow to family finances. Tickets, dresses, tuxedos, flowers, a trip to the beauty salon, sometimes a rented limo can add up to well over $1,000. But experts say there are ways to keep expenses down. One suggestion: Think as a group. "Get kids together in a group. It's a trend anyway for four or five couples or a group of kids to go to the prom together. So parents can be smart consumers and get better deals as a group," said Christina Ferrari, executive editor of YM, a magazine aimed at teen-age girls. For example, if five girls are getting their hair done, ask a salon for a group rate. If several couples are going out for dinner, ask the restaurant if it will prepare a fixed-price meal. Dresses, usually the most important piece of prom regalia, can cost several hundred dollars. Luckily, the hot style this year is the slip dress, which generally is less expensive than a formal gown. According to a survey by Your Prom magazine, the average purchase price of a gown last June was $199. Girls on average bought their gown 10 weeks in advance. For boys, about 85% of whom will rent their formal wear, the average rental price was $93. According to Your Prom, other average costs for girls include $36 for shoes, $31 for lingerie, $10 for hosiery, $34 for accessories, $23 for makeup and toiletries and $13 for a boutonniere. For boys, average expenses include $44 for tuxedo accessories and shoes, $19 for a corsage, $50 for dinner, $45 for prom tickets and $149 for a limousine.