if you want to try another free program, try 123D Design by Autodesk. Not that difficult to learn, especially with some good tutorial videos like the series put out here: https://www.youtube.com/watch?v=0TLalw3cQ08 (1st one of the series)
I use 123D for a LOT of my modeling needs because it is so simple to use once you understand the tools. You just need to think in the basic shapes and how to put them together to create what you are after.
It also has sketching abilities, both straight line and spline (curves), and an offset tool for shrinking/expanding unusual/odd shapes evenly. once you have your sketch how you want it, simply select it & extrude, then modify to suit your needs.
There are dozens of other free programs out there as well, google search and research are your friends.
There really aren't any modeling programs that will cost less than $30, sorry.
All the big names are thousands of dollars, unless you are "student" and qualify for a student version...(each has different requirements, so research)
the only "paid" one I have found that is pretty powerful for its cost is AC3D - under $100, but is really quite versatile. I am still learning how to use it and as yet, haven't really even scratched the surface, but I was able to modify an existing STL file to suit my needs using the free 14 day trial (bought it because of this), and I have successfully created a rather complex model by using a background image to "trace", and printed it. (ruger firearms logo - just the bird part - working on adding the "R" inset)
It does have a rather steep learning curve, but it isn't impossible (hey, if I can figure it out...lol) - doesn't have as many tutorial videos either, so yeah, a little more challenging.
SD4 #1 & #2 - Lawsy carriages, E3D v6, Rumba controller board, mirror bed plate, X motor fan, upgraded PSU & Mica bed heater
SD4 #3 - in the works ~ Folgertech FT-5, rev 1
Printit Industries Beta Tester - Horizon H1