<a href="#" class="buybtn">
  <span class="buybtn-text">
  Купить
  </span>
  <span class="buybtn-hidden-text">
  150$
  </span>
  <span class="buybtn-image">
  <span></span>
  </span>
  </a>

a {
  color: #FFFFFF;
  text-decoration: none;
}
.buybtn {
  -moz-transition: all 0.3s linear 0s;
  background: -moz-linear-gradient(center top , #FF8400 0%, #FF6600 100%) repeat scroll 0 0 transparent;
  border: 1px solid #FF5A00;
  border-radius: 5px 5px 5px 5px;
  box-shadow: 0 1px 1px rgba(255, 255, 255, 0.8) inset, 1px 1px 3px rgba(0, 0, 0, 0.2);
  clear: both;
  display: inline-block;
  float: left;
  font-family: Arial,sans-serif;
  height: 45px;
  margin: 10px 0;
  overflow: hidden;
  padding-left: 20px;
  padding-right: 65px;
  position: relative;
}
.buybtn-text {
  -moz-transition: all 0.2s linear 0s;
  color: #6E1D08;
  display: block;
  font-size: 18px;
  padding-top: 10px;
  text-shadow: 0 1px 1px rgba(255, 255, 255, 0.3);
  white-space: nowrap;
}
.buybtn-hidden-text {
  -moz-transition: width 0.3s linear 0s;
  background: none repeat scroll 0 0 #6E1D08;
  box-shadow: -1px 0 1px rgba(255, 255, 255, 0.4), 1px 1px 2px rgba(0, 0, 0, 0.2) inset;
  color: #FFFFFF;
  font-size: 18px;
  height: 100%;
  line-height: 42px;
  overflow: hidden;
  position: absolute;
  right: 52px;
  text-align: left;
  text-indent: 17px;
  text-shadow: 0 -1px 1px #363F49;
  text-transform: uppercase;
  top: 0;
  white-space: nowrap;
  width: 0;
}
.buybtn-image {
  border-left: 1px solid #FF5A00;
  box-shadow: 1px 0 1px rgba(255, 255, 255, 0.4) inset;
  height: 100%;
  position: absolute;
  right: 0;
  top: 0;
  width: 52px;
}
.buybtn-image span {
  -moz-transition: all 0.3s linear 0s;
  background: url("http://umasters.ucoz.ru/_ld/0/52139911.png") no-repeat scroll 75% 55% transparent;
  height: 38px;
  left: 50%;
  margin: -20px 0 0 -20px;
  opacity: 0.7;
  position: absolute;
  top: 50%;
  width: 38px;
}
.buybtn:hover .buybtn-text {
  color: #FFFFFF;
  text-shadow: 0 1px 1px #5D81AB;
}
.buybtn:hover .buybtn-hidden-text {
  width: 100px;
}
.buybtn:hover .buybtn-image span {
  opacity: 1;
}
.buybtn:active {
  background: none repeat scroll 0 0 #FF5A00;
}