My suggestion would be a Cosco Touriva/Scenera 5-point for about $40-$50. IMO the seats in the $125-$150 range aren't worth the extra money over the Touriva.
I'm sorry she can't afford a Britax now. Since her son needs a new seat right away I would suggest getting the Touriva/Scenera. Maybe she can save her money for a Britax Marathon later. Aside from being comfy and easy to use, it harnesses kids until they are ready for a booster, even if they are tall or heavy. Many kids are in it until 6 or 7, and at that point it would be expired anyway. Since her son is no longer a newborn, she should be able to install it fine in a small car.
There are a couple of new seats coming up that cost less than $200 and harness kids past 40 pounds also. She could look at those when they come out if she gets the Touriva/Scenera now.
I would definitely steer her away from the Cosco/Safety 1st Alpha Omega 3-in-1 seats. My friend has two and they are harder to install than my Touriva. Also, she ended up having to convert it to a booster when her very short son had just turned 3. Frankly, they are too expensive. You could buy a Touriva/Scenera and then a high-backed booster like the Graco TurboBooster for less than $100 total, and that is all the Alpha Omega is, except it is not as good a booster as the Graco. I'm just putting this in because it seems like the Alpha Omega is the first seat people look at when they want a seat that lasts a long time.
It is true the Touriva/Scenera doesn't have quite as much padding as some others, but my son never minded. My daughter did a little, but she didn't like my friend's Alpha Omegas either. She's also not that crazy about the built-in seat in our van. But she loves her Marathon.
If your friend is really on a budget, I would go for the Touriva/Scenera. Of the 40-pounds and under convertibles I feel it is the best value out there.
HTH,
Julie