Because correcting 2nd grade homework can be tedious.

better_cost_of_words.rb

# This one is smaller with more ruby magic.
# I love you case statement.

words = %w( too two bargain treasure American America nearly advice advise newspaper
Christmas Christ length long strength strong popular interest destroy comparison
compare disaster beneath cocoa guard island cousin cabbage eager )

longest = words.inject(0) { |length, word| word.size > length ? word.size : length }

char_cost = lambda do |char|
  case char
  when /[AEIOUWYaeiouwy]/ then 0.05
  when /[DHLNRSTBdhlnrstb]/ then 0.10
  when /[CFGMPVcfgmpv]/ then 0.15
  when /[JKQXZjkqxz]/ then 0.25
  end
end

words.each do |word|
  price = word.each_char.inject(0) { |total, char| total + char_cost.call(char) }
  puts "%-#{longest}s %0.2f" % [word, price]
end

cost_of_words.rb

words = %w( too two bargain treasure American America nearly advice advise newspaper
Christmas Christ length long strength strong popular interest destroy comparison
compare disaster beneath cocoa guard island cousin cabbage eager )

cost = {
  /[AEIOUWYaeiouwy]/ => 0.05,
  /[DHLNRSTBdhlnrstb]/ => 0.10,
  /[CFGMPVcfgmpv]/ => 0.15,
  /[JKQXZjkqxz]/ => 0.25
}

longest = words.inject(0) { |length, word| length = word.size if word.size > length; length }

words.each do |word|
  price = word.each_char.inject(0) do |total, char|
    cost_key = cost.keys.detect { |key| char =~ key }
    total += cost[cost_key]
  end

  puts "%-#{longest}s %0.2f" % [word, price]
end

out.txt

too        0.20
two        0.20
bargain    0.60
treasure   0.60
American   0.70
America    0.60
nearly     0.45
advice     0.55
advise     0.50
newspaper  0.80
Christmas  0.90
Christ     0.60
length     0.60
long       0.40
strength   0.80
strong     0.60
popular    0.65
interest   0.65
destroy    0.55
comparison 0.95
compare    0.70
disaster   0.65
beneath    0.55
cocoa      0.45
guard      0.45
island     0.50
cousin     0.50
cabbage    0.65
eager      0.40