You should carefully pick up a VPS plan from a very reliable service provider.
256 MB of RAM is absolutely useless for a VPS with a control panel such as PLESK or HELM. 256 RAM will not serve any purpose. You cannot install additional softwares with this amount of RAM such as ASP.NET 2.0. Naturally, your service provider will ask you upgrade within 1-2 days of purchase.
384 MB will be suitable but again the cost factor will be more. If you go for a control panel such as HELM then you have to invest more for webmail, SQL Server etc. Plesk on the other hand comes with all the required softwares for webmail and also MSDE.
At present, the price for 512 MB VPS crosses 1000 USD per year and this is expensive. You will have to provide all your profit every year to your VPS provider.
So judge carefully and select a VPS hosting plan.