I use this one for mssiah and it works fine.

I wonder if I could make my own, using some kind of pic or avr.

http://www.dealextreme.com/details.dx/sku.730
I've bought this one for midines. Works fine for a few minutes, then stops playing lower notes on square channels (it always jams when I start the song, never in the middle). Only action to unjam it is to power off and on my NES.
Also, there are occasional glitches and lags.

So with a bit of luck, you might work with it for a while, but for my final recording I always plug my midines into Axiom 61's MIDI OUT, that way it works flawlessly.

Those are cheap, for sure.

Depends how good you need your timing really.  Cheaper ones might suffer from alot of jitter, but that might not matter to you.

I would personally always recommend Midiman/M-Audio for midi interfaces.  M-Audio dip into alot of different markets now, not always to their credit, but MIDI and Audio Interfaces are things they truely excel in.

I have a Midisport 2x2 and my musical partner has a Midisport 1x1 (and an Oxygen 8).  They've both worked for 10 years without any problems.

I've used a Midisport Uno for a while and it's worked out well for me.  It's a bit more than the interfaces you listed above, but it's solid.  I'd check ebay for the best prices.

http://www.dealextreme.com/details.dx/sku.11277
http://www.dealextreme.com/details.dx/sku.730

These any good?

If not, could someone recommend a nice cheap one please