The most common pickups for violin are piezo or condenser.

Well, it depends on how cheap it has to be, for still managing "good".

Some condenser mics that aren't all that bad can run less than even the inexpensive commercial violin pickups. 

For example, consider this pickup at 65$ USD from Fiddlershop.com

http://fiddlershop.com/super-s.....ame=pickup

And then look at this condenser mic at about 50$ USD from Amazon

qid=1417102852&sr=8-13&keywords=usb+condenser+microphone

So it isn't necessarily less expensive to go with a pickup than something like a studio condenser mic. 

If both of those options are more expensive than what you are hoping for, there are some lower cost things you can try.  But the lower you go in price, the more you risk getting something that won't be as good as you want.

Some members here have gotten pickups off ebay.  I've thought some of those sounded pretty good.  But again, you're kind of taking a chance there, since the seller may not take it back and give you a refund just because you don't like it.

Or there are some super cheap possibilities we explored a while back, for DIY.  They had varying degrees of success, but they were experiments in the very low price range.  Some of them actually didn't sound too bad, and *maybe* would be an improvement over the mic on your phone or computer.

https://fiddlerman.com/forum/r.....2-or-less/

https://fiddlerman.com/forum/r.....or-violin/

https://fiddlerman.com/forum/r.....-a-violin/

I don't want to start a huge controversy, so let me start this next statement by saying that it is strictly my personal opinion.  I have not heard many if any piezo type pickups that I felt actually sounded like the acoustic instrument.  They are more of an electric instrument sound, and specifically a piezo electric instrument sound.  That can be great if it is what you are looking for.

The best luck I've had with preserving what I consider the acoustic instrument sound so far has always been from using mics.  For recording single acoustic instruments, I prefer large diaphragm studio type mics, with FET pre-amp if it is an option.  For strictly computer based recording, the ones that plug right into a USB jack and don't need any other gear are probably one of the better options for beginners.  Not real hard to get decent sound with those.

Another factor is if you are maybe an electronics hobbyist.. Most of the DIY options that were super cheap could have actually sounded much better with a little bit of preamp and/or tone shaping circuitry.  But unless you know how to build that sort of thing, it can get expensive fast and hard to find what you actually want.  The DIY experiments were mostly for folks that might just want to try pickup type gadgets (including small condenser mic mounted on the violin in some way) to see if it works well enough for them or if that is a direction they might like to look further in.

Anyway, hopefully that gives you some food for thought, augustoad.

Glad if it was of any help at all, augustoad.  I had noticed you are in Brazil, so I didn't assume Fiddlershop or Amazon would be the best prices for your part of the world.  They were just handy places to show typical examples of the gear I was talking about.

Sorry to hear about your guitar savings getting depleted.  But if there is one place to spend a little more if you can, I'd say the microphone is a good place to do it.  Being able to capture the sound of the instruments well is just one of those things where you may end up thanking yourself many times.

The next thing to look at (if you want an idea to think about for that) would be good headphones.  "Good" does not have to mean expensive.  Headphones that are comfortable, cover a wide range of sound well, and seem well enough made to last you a good while are what I mean by "good".

Comfort is a personal thing, where I don't think anyone can really tell you what is best.  Just try to remember that you may end up wearing them for many hours sometimes.  So far as being made well enough to last, again, you can figure that out yourself, really. 

Sound range, I can give a little help with, though..

That sort of test is handy for hearing which headphones you may try actually deliver sound you can hear over their range.  What a manufacturer or seller says the range is and what it actually is can be very different.

Often friends or family will have a spare set of headphones or two around that they might give you or sell much cheaper than buying a new set.  Or maybe they will let you try a set they don't want to sell or give away, just to see if you want to get the same kind they did.