I want to buy a ISO 400 film for photography, and I know Portra400 is good but I would prefer any cheaper alternative, as I am going to burn a lot.
Film photography is more expensive and more hassle than digital photography. Therefore, don't do initial learning with film. Learn the basics with digital. Once you get the equipment, the incremental cost of a picture is basically 0, unlike with film. You can learn about general exposure, framing, shutter speed effects, depth of field effects, and the like just with digital. These issues are the same whether the sensor is a piece of film or a piece of silicon.
After you've learned the basics, if you still really want to, then you can experiment with film. At that point you should already have a good feel for whether a shot you are considering taking has a chance of coming out or it's not worth bothering with. You want to try film after the "burn a lot" initial learning phase.
Even more with than digital, good film photography has a lot to do with knowing when to walk away.
For trying out film photography, buy the cheapest, non-expired ISO 400 colour negative film you can find - in an attempt to keep costs down. Sure, you can buy Portra if you want, but no film will make up for a poorly-exposed shot (for example). Good results can easily be achieved with Kodak and Fujifilm's cheaper films.
Learn to be frugal with your photos. Don't "burn a lot".
Note your settings, so that when you see the results, you can see what worked and what didn't.
Osullic's answer is good, but a couple more points:
Try lots of different films. If you want to get into film photography the bets thing about it is the different feel each film has. You might end up loving Portra (I do) but you won't know until you try!
I would say that learning to be frugal is a good idea, but while learning it is indeed difficult. For me, in the UK, the development and scanning is the cost, not the film, so "burning a lot" will cost a lot - so it's worth trying to avoid that.
However, having said that - if you see a shot that you think will be great, then burn a few ON THAT SHOT - you won't get any feedback on if your metering (manual or otherwise) was right, so if it's a scene you really want, then bracket - take a series of shots of varied exposure either side of what you think is right. This has saved a shot for me more times than I can count - especially important if you are into all-manual vintage cameras.
I have never noted settings to be honest as it's a right pain, but one suggestion would be to take a quick second shot of the scene with a digital, tweaked to be close enough to what you want that the EXIF will give you an idea of what to aim for if you really screw up. Even a smartphone will be good enough for this in most cases.