gistfile1.rb

# Equipment model
class Equipment < ActiveRecord::Base
  def price
    read_attribute(:price).to_i
  end
end

# Form _form.erb
<%= f.fields_for :equipment do |builder| -%>
  <%= render "equipment_fields", :f => builder %>
<% end %>

# Partial _equipment_fields.erb 
<div class="equipment_fields">
  <%= f.text_field :price %>
</div>