To add to what [MENTION=510310]ChrisAlbertson[/MENTION] has already said there are a lot of printers in the $200 range that are very good machine. The Creality ENDER line is a well regarded printer as well as are the Anet's. The key though it patience, because a 3D printer is not a plug and play type of device. You will seem to forever tinker with it to bet the best prints possible out of it. Then there is the learning about CAD software and Slicing software and types of filament, etc.

Cad is generally classified by the knowledge set you already have and also whether it is free or comes with a real cost. I focus on the free ones, personally.

If you want a browser type of CAD (no need to install on your PC or Mac) there are products like Tinkercad (this does require you to have an online account with AutoDesk which is free). It is one of the most popular educational CAD tools and one of the best for beginners to use. Its interface is friendly and easy-to-use. Tinkercad is ideal for 3D printing because it saves objects as STL files and offers solid or box modeling parameters for 3D printing geometries. Another great feature is that it’s completely web-based, so no downloads are required.

Then another free CAD program is SketchUp. It is one of the most intuitive and powerful free CAD tools available on the market. The combination makes it ideal for beginners and intermediate users. The platform is also completely compatible with the needs of anyone looking to 3D print. SketchUp boasts a 3D Warehouse, which has lots of pre-made models, including ones made for 3D printing.

Fusion360 from Autodesk has already been mentioned and is also the same CAD software I use.

All of the above products are proprietary and their licensing models could change in the future.

Now a short list of the really free as in Open Source Software (OSS)

Probably the best of the OSS software is FreeCAD. FreeCAD is a free, open-source parametric CAD software modeler. It’s considered to be a great entry point for designers and mechanical engineers new to the modeling world. Parametric modeling means that one can modify a 3D model by browsing the model history and adjust or change individual elements (this is how Fusion360 modeling is based). The graphical user interface may not look as polished as its competitors, but FreeCAD is ideal for precision design, which is good for technical and replacement parts.

If you are mathematically inclined there is OpenSCAD. In OpenSCAD you are basically defining your models with mathematical equations rather than primitive shapes. It is more akin to programming than modeling. It is a script-only based modeller that uses its own description language; parts can be previewed, but it cannot be interactively selected or modified by mouse in the 3D view. An OpenSCAD script specifies geometric primitives (such as spheres, boxes, cylinders, etc.) and defines how they are modified and combined (for instance by intersection, difference, envelope combination and Minkowski sums) to render a 3D model. As such, the program does constructive solid geometry (CSG). OpenSCAD is available for Windows, Linux and OS X.

If you are a Right Brained person and into more artistic expression or organic shapes, there are a lot of people modeling with Blender. For many, Blender is the epitome of 3D computer graphics software, not necessarily because it’s the best but because it’s free, open-source, and has a plethora of features and use cases. Examples include 3D modeling, texturing, rigging, skinning, smoke simulation, particle simulation, animation, rendering, and video editing. Naturally, Blender is more than capable of producing models for 3D printing. That said, unless you’re keen on diving deep into the platform, you might want to consider a different tool. Blender is considered to be a difficult tool to master, and the many features can make it both intimidating and confusing.

Just some closing thought; If you get a 3D printer, visit the communities that support whatever printer it is, ask a lot of questions, watch YouTube videos about the printer. Learn about the different types of filaments (ABS, PLA, PET as examples). Pick a CAD software and stick with it. You can also go to file repositories such as Thingiverse to see, download and print thousands of models designed by other people like yourself. That is exactly how I started my journey.

One more thing, printing with these consumer grade printers for parts to fit on your bicycle can be challenging. so make sure you learn the ins and outs of your printer very well, 3D printing is the easy part, but getting a 3D print to be precisely the size you want is what is hard.