I run a small business, a software development company and sell the software products I developed myself. Being an engineer rather than a salesman, I find it challenging to my market software.

I have 2 types of product:
1. specialised communication libraries
2. Business software, such as invoicing software.

The first type, beign a pretty unique and difficult to implement product, seems to sell well without a lot of effort put in promotion, But the second type I really have problem with.

Can anyone recommend how to attract lots of traffic to the invoicing software product page?

I have tried google adwords, but it works out too expensive. often 1.50 euro per one click. It is not a guarantee that people coming from there will always download the trial version.

Press releases? Would that be effective?
Any advice is very welcome

I think you should really try giving Google AdWords another try. Based on what you're saying, it's your best option to reach your very targeted audience and can get up and running with a small budget (which cannot be said for most other forms of advertising).

I think that your problem was that you simply weren't optimizing your AdWords campaign. Read up on AdWords and you'll be able to set something up spending no more than a very few US cents per click.

Google adwards is the best for appraching some millions of customer..

Google adwards is the best for appraching some millions of customer..

Yes, I keep hearing that, but so far it has not worked for me.

I am thinking of trying to hire a marketing specialist for this one specific job - to find correct keywords to use in adwords ad.