Speaking of house rules and times per day items, here's something I've seen used before. First, let's take a look at the simple mechanics of times per day items. A 10,000 gp magic item is effectively worth 2,000 gp per use per day, right? So, useable 4/day, that item would be 8,000 gp. Useable 1/day, that same item would be 2,000 gp. Now, what I've seen is that a lot of DMs will freak out at the possibility that you can get a 10,000 gp effect for a limited duration for a very small cost, and usually, such items only really need a few rounds or minutes to function in the first place. So, here's what I saw.
Basically, figure up the initial cost like normal, at 1/5th per use, then apply a modifier as follows:
1/day: *0.2
2/day: *0.6
3/day & 4/day: as normal
Effectively, 1/day is twice as expensive as in the DMG, and 2/day is one and a half times as expensive as in the DMG, then everything else is priced as normal. Seems to work well for DMs that don't like really low prices by using the times/day function.