Hi Dara,
Thanks for your question and here is my two cents worth of opinion.
Old Stanley planes can be very satisfying to use and Stanley generally set the standard for quality planes. Buying used can be a gamble when you cannot examine the tools in person, but it always means that you will need to do some work to tune them up. I enjoy doing that work but it can take a few hours to tune to it’s potential and not everybody wants to do that.
There are a couple of companies in North America that make excellent planes that work right out of the box. Buying from them gives you the certainty that your tool will work for years and you have access to their customer service if there is a problem. Of course, the best does not come cheap, but in my opinion, one working plane is better than three different sizes that are a challenge to keep in tune.
If you only want to buy one plane that you can use immediately and forever I would recommend the Low angle # 62 Jack Planes made by Lie Nielsen or the 62 1/2 by Veritas. There is a Lie Nielsen 62 at the shop and you should check it out. It is in the locked cabinet.
If you are still inclined to go the old plane route here are a few buying tips.
I think you made the right decision to max out at $70.00. Old number 5’s are pretty common and you will see plenty of opportunities to buy one in the future. At $70.00 It would have cost you $100.00 or more with shipping and tax. Buying older tools on ebay is challenging because one is not able to examine them really closely but here are a few tips based on my experience.
I looked at Stanley #5s on Ebay, saw a range of prices and saw several that should be rejected out of hand because of condition, damage or youthful age.
Try to find out how old the plane is. Most sellers will post pictures of each part of the plane and that is a help because you can look for cracks, dings and other damage as well as finding an approximate date of manufacture. Sometimes the seller will already know the type # which is very helpful for dating. The following link is to a very easy tool that can help you to identify the age of old Stanley planes
How to Identify Stanley Hand Plane Age and Type (Type Study Tool) | Wood and Shop
The best planes were probably produced before the second world war as demand and quality declined after that time. If you would like to borrow an old Stanley #5 I would be happy to lend you an old (c1907) one I have and rarely use these days. I would not sell it as it has a crack in the body, but it works very well.
I hope this is of some help and please do not hesitate to contact me if I can help further. Choosing a first plane is daunting, especially when you are buying used and if I can be help with advice or opinions, please don’t hesitate to contact me.