Several people have expressed dissatisfaction about how metamagic currently works, feeling that having to spend a feat on the metamagic should be enough cost, or at least that the increase in spell level is too high. I agree and disagree with them; I think there should be some sort of limiting factor on the use of metamagic, but the spell level increases and need to prepare them as metamagic makes them all but useless. Thus, I suggest the following alterations of the Metamagic Feats presented in the PH.

When casting a spell you wish to use a single metamagic effect on (for example, a Stilled Knock spell to open the shackles on your hands), you have the option of either increasing the amount of time necessary to cast the spell (as per a sorcerer or bard under standard metamagic rules; see page 78 of the PH), or spending an amount of XP as determined by the feat (see the descriptions below).

If you wish to use two or more metamagic feats upon a spell, you may either pay the full XP cost for each metamagic feat, or spend the additional time, plus XP for all but the cheapest feat. For example, to cast an Empowered, Maximized, Silent and Stilled Magic Missile will either cost you 175 XP, or require a full round action plus 150 XP.

When spending XP to metamagic a spell, you may not actually decrease your level. You may, however, enter into "XP debt" for the next level by going below the minimum for the current level. You will have to earn yourself back up to the requirement for the next level, including making up for all your metamagic XP drains. For example, Hennet engaged in an arduous spell battle right after gaining 5th level. While he is 5th level, the number of metamagiced spells he cast has drained him to only 9000 experience points. In order to reach 6th level, Hennet will still have to gain a net total of 15,000 XP. Magicians who wish to advance quickly in their craft are thus very careful about what they metamagic, lest they be left behind. In addition, magicians in XP debt are considered "fatigued", though XP debt alone will not make them "exhausted" (see page 84 of the DMG for these two conditions).

Empower Spell
Prerequisites: Spellcaster level 5th+
Benefits: As per the feat list on page 82 of the PH. However, rather than requiring the two additional spell levels, the caster must either take the extra time to cast the spell or spend 50 XP per spell level (25 XP for cantrips)

Enlarge Spell
Prerequisites: Spellcaster level 3rd+
Benefits: As per the feat on page 82 of the PH. However, rather than requiring the additional spell level, the caster must either take the extra time or spend 25 XP per spell level (10 for cantrips).

Extend Spell
Prerequisites: Spellcaster level 3rd+
Benefits: As per the feat on page 82 of the PH. However, rather than requiring the additional spell level, the caster must either take the extra time or spend 25 XP per spell level (10 for cantrips).

Heighten Spell
Prerequisites: Empower Spell, Able to cast the target level of spell
Benefits: As per the feat on page 82 of the PH. However, rather than requiring the additional spell level, the caster must spend 50 XP per _intended_ spell level. For example, if a fireball is to be cast at as a 4th level spell (to penetrate a minor globe of invulnerability), it would cost the caster 200 XP, not 150. One may not take additional time to cast a Heightened Spell.

Maximize Spell
Prerequisites: Spellcaster level 7th+
Benefits: As per the feat on page 83 of the PH. However, rather than requiring the additional spell level, the caster must either take the extra time or spend 75 XP per spell level (35 for cantrips).

Quicken Spell
Prerequisites: Still Spell, Silent Spell, Able to cast 4th level spells
Benefit: As per the feat on page 84 of the PH. However, rather than requiring the additional spell level, the caster must spend 100 XP per spell level (50 for cantrips). Taking extra time defeats the purpose of the feat.

Silent Spell
Prerequisites: Spellcaster level 3rd+
Benefits: As per the feat on page 85 of the PH. However, rather than requiring the additional spell level, the caster must either take the extra time or spend 25 XP per spell level (10 for cantrips).

Still Spell
Prerequisites: Spellcaster level 3rd+
Benefits: As per the feat on page 85 of the PH. However, rather than requiring the additional spell level, the caster must either take the extra time or spend 25 XP per spell level (10 for cantrips).

General Conversion for future feats: For each additional level a feat requires a spell to be prepared at, it requires 25 XP per spell level to use that feat, and roughly half as much for a cantrip. Thus, if a future feat required 6 additional spell levels, it would take 150 XP per spell level to use the feat.