@Cody Evans SEO's financial cost is the cost to build your site, or rent a site. You can test a service like InvestorCarrot or LeadPropeller. I pay $50 / one site. There's some higher payment plans if you think you need extra services - though that will increase your budget by up to $150 - no cheap amount if you're really focusing on one site. InvestorCarrot has solid customer service. There are some limits, but for the most part, I recommend it (i have no financial stake at all) because we're investors not web programmers.
One the issue of investors v. website managers, you also have to consider, when choosing whatever site you choose, if you go the route of having your own site designed (and there are plenty of reasons for that as well), if something breaks, you're going to have to keep hiring your web guy. That is likely annoying and time consuming. On the other hand, if you build your own site you have complete freedom: including getting an https as opposed to http, and word press plugins.
Although I haven't done a side by side dual test sites, my conversation rates have been off the charts on Google Adwords once everything was properly set-up 10 to 20% depending on the time periods (averaging around 15%). Google Adwords in my opinion is the ultimate test because you control your traffic. In SEO, lord knows who is finding my site. I get people from India trying to sell me their property. Maybe one day I'll be international!
As far as the costs to hire someone to manage your Google Adwords, I've seen quotes for around $400 to $1,000. I have no opinion whether that is worth it, it depends on too many things. If you have no idea what you're doing with no tech background, very well could be. That being said, $1,000 is essentially my goal monthly budget. So the concept of me paying half my budget to have my account overseen, doesn't seem particularly logical. Additionally, many "gurus" won't work with you unless your putting your budget in a decent range. It's definitely something you need to reach out to several services, find out their costs, how they will work with you, price minimums, evaluate your own ability - and take it from there.
In terms of how much does Adwords cost to actually do it, you have complete and total control. I would say tho, if you are spending less than $500/mo, it's hard to imagine getting much results in terms of deals. You could get lucky but it's math: say you spend $500 - you probably get 50 clicks ($10 is quite a low cost per click). You convert at say 10% (pretty good number) down to 5 leads. Getting a deal every 5 leads . . . nothing I've ever experienced.