You don't *find* cost-effective customer acquisition strategies, but design one per your internal capability, external niche, and dynamic of your operational market. The intent should be to serve across your capability than getting lured by others' growth. Likewise, you diversify to leverage either the cross-selling or upselling opportunity. Anything beyond these two gets counted as alternative product, something akin to completely different from your existing service span.

Secondly, you choose market diversification only when you're convinced that Market Penetration, Product Development, and Market Development aren't going to be the viable options. We're talking about companies with budgetary constraint. The diversification could be either concentric diversification- leveraging upon your technology prowess, or horizontal diversification- new product or up-selling product. Because, it may require new skill sets- not only technologically but also around marketing/sales/operations process- it's riskiest of all the four options as mentioned above.

Thirdly, in my decade of experience working with startup companies, or the ones at status-quo, I have seen people often confusing marketing to sales. That's problem inevitably comes first on the priority list. Ironically, a number of times, the problem comes out to be inadequate market planning, strategy designing, and poor execution around the existing product/service categories. I am assuming you would have brainstormed enough to reach the conclusion to diversify.

And yes, marketing takes time to provide return on investment. There may not be cost saving way to marketing, but optimizing the marketing effort and tactics around your budget.

Hope above proves to be of some help. Need any input in particular? I am just a clarity away!!